IRAM 300, rue de la Piscine38406 ST. MARTIN d’HERES (France)Fax: (33/0) 476 42 54 69

PROPOSAL FOR 30M TELESCOPEDeadline: 17 Sep 2009 Period: 01 Dec 2009 — 31 May 2010

For IRAM use

Registration N◦:

Date:

TITLEA Legacy Survey to Study Cold Gas Scaling Laws in the Local Universe

Type: Solar system: continuum i lines i other i Extragalactic: continuum i CO lines y other iGalactic: continuum i lines i circumstel. env. i young stel. obj. i cloud struct. i chem. i other i

ABSTRACTThe scaling laws of galaxies provide a quantitative means of characterizing their physical properties and the routeto understanding their formation and evolutionary histories. Current galaxy formation models predict that thescaling relations between the gaseous and stellar components of galaxies provide important information aboutformation processes (e.g. accretion) occurring at the present day. The study of cold gas scaling laws is currentlyseverely hampered by a lack of suitably large, unbiased samples of galaxies with accurate measurements of totalatomic and molecular gas content down to low enough levels to constrain the gas as a reservoir for future galaxygrowth. We propose to rectify the situation by obtaining IRAM 30m CO observations for a sample of ∼ 300galaxies uniformly selected from the SDSS spectroscopic and GALEX imaging surveys with deep HI data fromArecibo. We will make this legacy data set available to the entire astronomical community.

Is this a resubmission of a previous proposal ? no y yes i – proposal number(s): . . . . . . . . . . . . . . . . . . . . . . .Is this a continuation of (a) previous proposal(s) ? no y yes i – proposal number(s): . . . . . . . . . . . . . . . . . . . . . . .

Hours requested for this period:

∼ 100LST range(s): from: to: number of intervals:

from: to: number of intervals:

Special requirements: Large Program y pooled obs y service obs i remote obs y polarimeter i

Scheduling constraints: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Receivers: EMIR y HERA i Bolometer i Other i

List of Objects (give most common names)

( for additional sources which do not fit hereuse the \extendedsourcelist macro )

Epoch: J2000.0Source RA DEC VLSR

G3261 00:55:32.61 +15:46:33.0 z=0.03747G3504 01:18:23.44 +13:37:28.5 0.03801G3645 01:15:01.75 +15:24:48.6 0.03074G3777 01:23:16.82 +14:39:32.4 0.03959G3817 01:43:25.96 +13:51:16.8 0.04500G3962 02:03:59.15 +14:18:37.4 0.04274G3971 02:05:52.48 +14:25:16.3 0.04262G5442 11:00:32.52 +02:06:57.8 0.03939G6375 12:27:27.62 +03:18:07.7 0.04876G6506 12:43:09.36 +03:34:52.3 0.04867G7025 13:50:33.80 +02:13:56.0 0.04218G7031 13:46:47.19 +02:07:12.2 0.03305G7058 13:50:32.14 +03:11:39.0 0.03241G7493 14:27:20.13 +02:50:18.2 0.02644G7499 14:26:32.10 +02:45:06.0 0.03939G7561 14:33:35.68 +02:38:19.3 0.02827G9287 14:08:36.94 +03:25:22.7 0.04041G9301 14:03:16.98 +04:21:47.4 0.04623G9343 14:16:48.38 +03:37:48.2 0.04934

Principal Investigator:

Guinevere KauffmannMPAKarl Schwarzschildstr. 185748 Garching (Germany)Tel: (+49) 89 30000-2013 Fax: (+49)89 30000-2235Email: gamk@mpa-garching.mpg.de

Other Investigators (name, institution):

Carsten Kramer, co-PI (IRAM – Spain); C. Buch-bender (IRAM – Spain); B. Catinella (MPA – Ger-many); L. Cortese (U.Cardiff – UK); S. Fabello (MPA –Germany); J. Fu (SHAO – China); R. Giovanelli (Cor-nell – USA); J. Gracia-Carpio (MPE – Germany); Q.Guo (MPA – Germany); M. Haynes (Cornell – USA); T.Heckman (JHU – USA); M. Krumholz (UC Santa Cruz –USA); C. Li (MPA – Germany); S. Moran (JHU – USA);N. Rodriguez-Fernandez (IRAM – France); A. Saintonge(University of Zurich – Switzerland); D. Schiminovich(Columbia University – USA); K. Schuster (IRAM –France); A. Sievers (IRAM – Spain); L. Tacconi (MPE– Germany); J. Wang (MPA – Germany);

Expected observer(s) see management plan

join to this form: scientific aims ≤ 2 typed pages (≤ 4 pages for Large Programs) and ≤ 2 pages Figs., Tabs., and Refs.

Technical Summary

? EMIRNote that up to 4 IF signals can be recorded and up to 2 EMIR (always dual polarization) bands can be combined in one EMIR

setup. For a summary of EMIR connectivity consult the IRAM Granada home page or the Call for Proposals

TransitionsT ∗A = expected line antenna temperature; ∆v = required velocity resolution.

setup band species transition frequency T ∗A rms ∆v backend a)GHz mK mK km s−1

1 E0 CO 1-0 111.1975 3–30 0.8–10 30.0 Wa) V: VESPA, W: WILMA, 4: 4 MHz filterbank, 1: 1 MHZ filterbank

Observing parametersmap size in arcmin; T = requested telescope telescope time per setup

setup map size mapping switching T remarkNo. ∆x×∆y mode a) mode b) [h]

1 × none WSw 550 —Total EMIR time requested: 550

a) none, OTF (on–the–fly), R: Rasterb) PSw: position switching, FSw: frequency switching, Wsw: wobbler sw.

Observing time estimates: (Please read main text first) To estimate the total time required, weestimate molecular gas masses for each of the 210 galaxies in the GASS DR1 sample. Based on our pilotprogram results, we set M(H2) = 0.5 × M(HI) in cases where the HI line was detected. For non-detections,we assumed that we would need to integrate to the limit of M(H2) = 0.03 × M∗. We then estimated theCO line peak at the center of the galaxy, taking into account the luminosity distance of the galaxy, the HIline width and the galaxy size. Finally, we used the EMIR/30m observing time estimator to derivethe total amount of time required to obtain a ∼ 8σ detection in area under average winter/good summerconditions (pwv = 4 mm), an average elevation of 45◦, and 30 km s−1 channels. (We aim at a velocityresolution of 30 km s−1, because we would like to compare the CO linewidths with the HI linewidths in asystematic way as part of our scaling relations study). We also estimated the total time to be spent in offsetobservations assuming ICO(1−0)(offset)/ICO(1−0)(center) = 0.3 (fig. 5c). The total time (ton + toff) requiredto detect the CO line at the central+offset positions (when needed) of the 210 GASS DR1 galaxies wasdivided by the number of galaxies to estimate the average time per galaxy. This time was multiplied by afactor of 1.5 to include telescope overheads. We consider that this is an appropriate correction (comparedto the factor of 2 used in the time estimator) given the rather simple observing strategy described in theproposal. Under these assumptions, we will require on average 1.85 hr (σ = 1.2mK) to measure the totalmolecular gas mass of a galaxy. We thus require a total of 550 hr for the requested 300 galaxies, of which85% will be spent observing central positions and 15% in offset observations. We think this time requestis reasonable if spread over a multi-semester campaign running over a period of around 3 years, i.e. anaverage allocation of ∼ 100 hours per semester.

A Legacy Survey to Study Cold Gas Scaling Laws in the Local Universe

Perhaps the most fascinating aspect of nearby galaxies is the intricately interwoven system of corre-lations between their global properties. These correlations form the basis of the so-called ”scaling laws”,which are fundamental because they provide a quantitative means of characterizing the physical propertiesof galaxies and their systematics. Galaxy scaling laws also provide the route to understanding the internalphysics of galaxies, as well as their formation and evolutionary histories.

We currently enjoy a rich and diverse array of scaling laws that describe the stellar components ofgalaxies. The Tully-Fisher relation and the size-mass relation for local spiral galaxies play a crucial role inconstraining current theories of disk galaxy formation. These theories hold that disks form when gas coolsand collapses within dark matter haloes until it reaches centrifugal equilibrium. The observed size-massrelation is consistent with the idea that the angular momentum of the infalling gas originated from tidaltorques during the initial collapse of density perturbations in the early universe, and that this angularmomentum was largely conserved during the subsequent collapse of the gas to form the disk. It is alsoconsistent with the idea that disk galaxy formation continues right up to the present day (e.g. Fall &Efstathiou 1980; Kauffmann 1996; Mo,Mao & White 1998)

Likewise, the scaling laws of bulge-dominated galaxies (the Fundamental Plane) provide importantconstraints on how these systems have assembled through merging. The stellar mass-metallicity relationis fundamental to our understanding of the fraction of metals injected into the intergalactic medium bysupernovae-driven winds. The discovery of a close correlation between black hole mass and bulge mass ledto the idea that black holes may play an important role in regulating the growth of galaxies. Galaxy scalinglaws should not just be regarded as important in our understanding of nearby galaxies. Now that highredshift astronomers are switching from ”discovery mode” to more systematic studies of larger samples,attention is focusing on understanding if and how the scaling relations defined at low redshift have evolvedwith cosmic epoch.

It is remarkable, therefore, that so few well-established scaling laws exist describing how the cold gasis correlated with the other global physical properties of galaxies. The only well-studied scaling law isthe relationship between the formation rate of new stars and the surface density of cold gas in disks, theso-called Schmidt-Kennicutt star formation law. The star formation law, however, should be regarded as alocal scaling relation, not a global one. It serves to constrain the local physics of the interstellar medium,rather than the global galaxy assembly processes described above. There has been surprisingly little workto understand how the cold gas is related to global galaxy properties, such as their masses, sizes and bulge-to-disk ratios. This constitutes a serious deficiency in our knowledge, because the gas is the reservoir ofmaterial out of which stars form. As such, the gas ought to be much more sensitively linked to formationprocesses (e.g. accretion) that are occurring now, rather than integrated over timescales of many gigayears,as is the case for the stars. We now argue that the reason why so few scaling laws involving cold gas existin the literature and the reason why cold gas properties are not yet established as a fundamental constrainton galaxy formation theory, is simply the lack of suitable data.

What data are needed to define global scaling laws between gas and stars : The majorrequirements for defining scaling relations are the following:1) Homogeneous data and accurate measurements of all the physical properties under consideration.2) Each property must be measured in an unbiased way with respect to every other property, otherwisethe derived relations between the properties will themselves be biased.3) The measurements must span sufficient dynamic range so that one can properly categorize the full scaleof possible variation in each physical quantity.4) The sample must be large enough to define the correlations, both in terms of the mean and the scatterabout the mean.Nowadays, all 4 conditions listed above are routinely met by optically-selected samples of galaxies at lowredshift. In particular the Sloan Digital Sky Survey (SDSS) has obtained 5-band optical imaging data overa quarter of the sky, and high S/N spectra covering the wavelength range from 3800 to 9200 A with aresolution of 2000 for a sample of 700,000 galaxies. The SDSS will stand as the main Legacy Survey ofnearby galaxies at optical wavelengths for decades to come.

The study of atomic gas in nearby galaxies will benefit from a new generation of blind HI surveyscovering wide areas of the sky. The most advanced among these is the Arecibo Legacy Fast ALFA Survey(ALFALFA; Giovanelli et al 2005), which will detect more than 20,000 extragalactic HI line sources out toz∼0.06. Although ALFALFA survey data are accurate, homogeneous, and unbiased with respect to anyother galaxy property, the survey is shallow, with the the result that it does not probe a large dynamicrange in HI-to-stellar mass ratio for all but the very nearest galaxies.

Unfortunately, the situation with molecular gas observations of nearby galaxies is far worse. Homo-geneous and relatively deep data does exist in the form of molecular gas maps covering the optical disks

of 40-60 nearby galaxies (e.g.the HERACLES survey, Leroy et al 2009; Kuno et al 2007). These samplesare excellent for studying star formation laws within galaxies, but the number of galaxies is too small toadequately define global scaling relations.

Older data are beset with a variety of uncertainties and biases: 1) Single dish observations often didnot cover the entire disk of the galaxy and thus the total molecular gas content of the galaxy cannot bemeasured accurately. 2) The data are heterogeneous. The galaxies were selected for a variety of differentreasons, often using IR luminosity as a criterion. Any scaling relation is thus likely to be severely biased.3) Most existing catalogues only record detections and do not provide upper limits. As a result, it isimpossible to assess the true dynamic range in quantities such as M(H2)/M∗ or M(H2)/M(HI).

In recent work, Cheng Li assembled CO data from the literature for 374 nearby galaxies in the SDSSsurvey. The vast majority of these galaxies have redshifts less than 0.02. The measurements were thenplaced on a common scale, using a common conversion factor and cosmology. More details are given inhttp://www.mpa-garching.mpg.de/∼gamk/gasproblems.pdf. The resulting scaling relations are plotted inthe top panels of Fig. 4. The scatter is huge and Cheng’s analysis concludes that aperture problems arelikely one of the major underlying causes. In addition, different telescope calibrations, low S/N detections,selection on IR luminosity, and variations in the CO-H2 conversion factor (e.g. ULIRGs have a conversionfactor 5 times lower than the Galactic one that we assumed (Downes & Solomon 1998)) all artificiallyincrease the scatter.

One contribution to solving the problem: We are carrying out the GALEX Arecibo SDSS Survey(GASS), an ongoing large targeted survey at Arecibo, home to the world’s largest single-dish radio telescope.GASS is designed to measure the neutral hydrogen content of a representative sample of 1000 galaxiesuniformly selected from the SDSS spectroscopic and GALEX imaging surveys, with masses in the range1010 − 1011.5M¯ and redshifts in the range 0.025 < z < 0.05. Integration times are set so that weshould detect all galaxies with HI mass fractions of 1.5% or more. GASS will produce the first completesample of galaxies with homogeneously measured stellar masses, structural properties, star formationrates and atomic gas fractions measured down to sufficiently low levels to properly constrain the HI asa reservoir for future growth of galaxies in the local Universe. Observations started in March 2008, andare expected to be completed over a period of 3 years. More information is available at http://www.mpa-garching.mpg.de/GASS.

The first GASS data release (GASS DR1) consisting of 210 galaxies will take place once our first papers(which are currently close to completion) are accepted. In Figure 1, we plot relations between the averageHI-to-stellar mass ratio as a function of stellar mass and as a function of stellar surface density. The stellarsurface density is proportional to M∗/R2

eff ; we are thus probing the size dependence of the HI gas fractionat a given stellar mass. Interestingly, there is a strong dependence of HI fraction on surface density above3 × 108M¯ kpc−2, a value that was identified in Kauffmann et al (2003) as marking a definitive “break”in the scaling relation between surface density and stellar mass.

This Proposal: One intriguing hypothesis to explain why smaller, denser galaxies have lower HIfractions, is that a larger fraction of the cold gas reservoir is in the form of molecular gas (e.g. Krumholz,McKee & Tumlinson 2009a,b; Obreschkow & Rawlings 2009). If true, this has important implicationsfor understanding the nature of the cold gas in ∼ L∗ galaxies at higher redshifts, which are predicted bytheory and also observed to have higher surface densitites that their local counterparts. Our new theoreticalmodels (Jian Fu et al, in preparation) also demonstrate that the exact position of a galaxy on the coldgas scaling relations is a sensitive diagnostic of both its angular momentum and of the fraction of gas thathas recently accreted from its surroundings. It is well known that cold gas consumption times in localspirals are short compared to the age of the Universe – galaxies are predicted to transition through therelations following each new accretion episode. Depending on the angular momentum of the infalling gas,an accreting galaxy can start out as either HI-rich or H2-rich, and then migrate down to the gas-poor partof the diagram (Fig. 4). Cold gas scaling relations should thus be regarded as dynamic rather than staticand they provide important insight into galaxy growth at the present day.

We believe that our understanding of cold gas scaling laws will not be complete with HI surveys alone.We also need to understand if and how the balance between atomic and molecular gas changes across thelocal galaxy population. We are thus proposing to follow up a minimum of 300 galaxies targeted by theGASS survey with the IRAM 30m telescope. Our proposed survey will provide a definitive census of thepartition of condensed baryons into stars, atomic and molecular gas in 0.1 − 10L∗ galaxies in the localUniverse. It will also meet the 4 major criteria necessary to define robust scaling laws between thesequantities:1) Galaxies in the redshift range 0.025 < z < 0.05 (i.e. ∼ 100 to 200Mpc) have angular diameters thatare small enough to enable accurate recovery of the total CO line flux with a single IRAM 30m pointingfor the majority (80%) of galaxies. For the remaining 20%, simulations demonstrate that we will be able

to measure the total molecular mass by adding a single offset pointing and assuming azimuthal symmetry.By targeting galaxies with stellar masses greater than 1010M¯, we will be concentrating on the populationof galaxies where the CO line flux is most likely to provide a reasonably accurate measurement of the totalmolecular gas content using a single conversion factor. Of course we will need to look for any indicationsthat this assumption breaks down for subsets of the galaxies in our sample. Information on metallicity anddust content of the galaxy are provided by the SDSS spectra, and this should help.2) Our sample will be selected randomly from the GASS sample, and will thus be unbiased.3) We will integrate until the CO line is detected, or until we reach an upper limit in molecular gas massto stellar mass ratio of 0.03 (i.e. similar to that achieved by the GASS survey for the atomic gas.)4) A survey of about 300 galaxies has been demonstrated to be sufficient to determine accurately a scalingrelation involving three variables, as well as to measure the scatter around the relation ( see for examplethe Jorgensen et al. 1996 Fundamental Plane survey of elliptical galaxies in clusters).

Results from our pilot observations: In the last proposal round, we were granted 80 hours ofobserving time (project 123-09) to carry out a pilot study of molecular gas in 15 galaxies with stellar massesgreater than 1010M¯, atomic gas fractions greater than 10%, redshifts in the range 0.025 < z < 0.05, opticaldata from SDSS and HI data from Arecibo. The pilot program galaxies span a wide range in colour fromNUV-r values characteristic of galaxies with passively evolving stellar populations, to very blue galaxieswith clear ongoing star formation.

The observations were carried out in June and August 2009 under poor but stable weather conditionsof about 10 mm of pwv. Even so, we detected 70% of the galaxies and imposed strong constraints tothe molecular gas mass fraction for the non detections (M(H2)/M∗ ≤ 0.03) (see fig. 3). We also spent asignificant amount of the time observing offset positions to characterize the extent of their molecular gasdistributions and to find the most efficient way to correct for aperture effects (fig. 5).

Observing strategy: We base our observing strategy on the knowledge acquired from the pilotprogram. This strategy is designed to reduce telescope overheads as much as possible:* Thanks to the large frequency bandwidth of the new generation receivers (∼4GHz = 11000 km s−1 atthe average redshift of the GASS sample) we can observe the redshifted CO(1-0) line in all our samplegalaxies with a single tuning of the receivers. We will save 20–30 min per source this way. This singletuning strategy will also be extremely useful to characterize any possible calibration variations betweendifferent atmospheric conditions/observing runs, because we always look at the same lines of the selectedline calibrators. The single tuning frequency covers the range from from 109.1 to 113.1 GHz, so we profitfrom a considerably improved atmospheric transmission as compared to the CO rest frequency. Finally,we note also that the 13CO(1–0) rest frequency lies in the observed frequency band and we can thus doline calibration using carbon stars or other nearby strong sources.* GASS galaxies are concentrated in a strip with R.A. = 10–16 hr and Dec. = 0–15 d (see fig. 2). Thatmeans that if a galaxy is detected quickly, it will be possible to start to observe a nearby galaxy using thepointing corrections from the previous one.* We will accommodate to the changing weather conditions by observing blue galaxies (which are expectedto be bright in CO) under poor weather conditions (i.e., high pwv), and red galaxies and offset positionswhen the weather is good.* Because there is a large sample of galaxies to choose from, we will always be able to observe at highelevations of about 45 deg on average (i.e., low atmospheric opacities).* A central pointing will be sufficient to provide an accurate total molecular gas mass in most cases (80%,fig. 5a). We have used a compilation of 46 nearby galaxies with high-quality CO(1-0) maps as a set oftemplates for estimating aperture effects. We place these galaxies at the redshift of the galaxies in theGASS DR1 sample and compute the fraction of the total line flux that would be recovered within the 22”beam of the 30m telescope (see fig. 5). This gives a criterion on the angular size of the galaxy, above whichan offset observation is required to accurately recover the total flux. Galaxies with optical sizes larger than40” with strong central CO(1-0) lines will require an additional offset observation (at a distance 0.75×Beam∼ 16” from the center, fig. 5b). Large galaxies where the CO(1-0) line is weak are mainly early-typegalaxies with red colours. Our pilot program demonstrated that such galaxies are never detected in theoffset position, even when they have high atomic gas fractions. We will not observe offsets for these objects.

Observing time estimates: (please see the technical summary on page 2 for detailed justification)We require a total of 550 hr for the requested 300 galaxies, of which 85% will be spent observing centralpositions and 15% in offset observations. We think this time request is reasonable if spread over a multi-semester campaign running over a period of around 3 years, i.e. an average allocation of ∼ 100 hours persemester.

Additional Science: There are many scientific applications of a large CO survey. Here we provide abrief summary of just a few of the possibilities:

• An accurate CO luminosity function for massive galaxies. Existing CO luminosity functionshave been derived using incomplete and inhomogeneous data sets (Keres et al 2003; Obreschkow & Rawlings2009). The selection function of our survey is extremely well determined; this will enable a definitive COluminosity function to be constructed for galaxies with M∗ > 1010M¯.

• The CO linewidth as an estimator of dynamical mass. It has been claimed that HI and COlinewidths track each other very closely, but this has not been tested using galaxy samples that span awide range in physical properties. We can also study the relationship between the total baryonic mass ofgalaxies (stars+cold gas) and their dynamical masses.

• Relations between star formation, atomic and molecular gas on galactic scales. Scalingrelations between star formation and gas surface density have been studied in detail for small samples ofnearby spirals. How well do the results extrapolate across the whole galaxy population? Ancillary UV datafrom GALEX and IR data from Spitzer/Herschel can be combined with our HI and CO data to answerthis question. We can also search for any molecular mass that is undetected in CO (e.g. because it isphoto-dissociated) by comparing with the molecular mass inferred from the IR.

• Do AGN influence the cold gas in nearby galaxies? The SDSS spectra provide very usefulinformation about the AGN content of the galaxies in our sample – around 30% of the galaxies in oursample have a central LINER or Seyfert nucleus.

• Morphology of the gas. In galaxies where he have offset observations, we will have an estimateof the concentration of the gas. The expected (local) pointing accuracy is about 1′′, allowing us to studyasymmetries in the line profiles and ask whether they are correlated with other properties of the galaxies,such as their star formation rates.

• Molecular gas in elliptical galaxies. Even if we do not detect the CO line for individual objects,the spectra can be stacked and one can still derive average molecular gas fractions for classes of galaxiesthat are gas-poor, such as ellipticals.

Program Management: Our team of multi-wavelength observers and theorists encompass a widerange of expertise and talents that will allow us to make sure that this data set is of lasting legacy valuefor the full astronomical community.

** G. Kauffmann and C. Kramer will be responsible for the overall program management and coor-dination. They will maintain communication to IRAM, as well as teams from the two other facilities(ARECIBO and GALEX) that are involved with the GASS program. Communication will be enhanced byregular team meetings. A dedicated project wiki portal will be created, to inform the public, and to allowall Co-I’s to coordinate their work in an efficient way (see, for example, the GASS portal http://www.mpa-garching.mpg.de/GASS/)

** A. Saintonge, J. Gracia-Carpio and L. Tacconi will be in charge of the observations, data reductionand analysis. They will be aided by a team of observers (Buchbender, Catinella, Fabello, Li, Rodriguez-Fernandez, Sievers). We hope to carry out a substantial fraction of the observing remotely from Garchingor from IRAM, Granada. The involvement of experts from IRAM will ensure a uniform and homogeneousdata product.

** We suggest that this project be scheduled during the pooled weeks, as a poor weather backupproject. Our pilot study clearly showed that we can detect significant fraction of the galaxies, even whenthe amount of pwv is high. One of the advantages of using the pool and its database is that logs areautomatically created and the project progress can easily be followed. We will also staff the pools.

** We have substantial experience and expertise in the acquisition, processing and analysis of ancillarydata. B.Catinella and D.Schminovich lead the processing of the HI observations of the GASS sample, andwork closely with R.Giovanelli and M. Haynes on the interface between GASS and ALFALFA. J. Wang isexpert on photometric processing of GALEX and SDSS data. S. Moran leads an effort to obtain follow-uplong-slit spectroscopy for the GASS sample. L. Cortese is planning to work on Herschel observations thatwill cover many galaxies in the GASS sample.

** Our team includes theoreticians (PhD student Jian Fu, Qi Guo, Kauffmann, Krumholz) who arebuilding new galaxy formation models that track the evolution of both atomic and molecular gas in theMillennium Simulation (see Fig. 4).

** We expect that the initial scientific analysis and exploitation of the data be led by the postdocs andstudents working in consultation with the more senior members of the team.

** After acceptance of the first set of papers, our intention is to release the data in user-friendly, VO-compatible form to the entire astronomical community in a series of yearly data releases.

Figure 1: Recent results from the GASS HI survey. We plot the average value of the HI-to-stellar mass ratio as a function of stellarmass (left) and stellar surface density (right). The difference between the red and the green symbols indicate the remaining uncertaintythe mean scaling relation due to HI non-detections. The blue points are galaxies detected by the ALFALFA survey in the same redshiftrange. Clearly the ALFALFA galaxies are biased towards very HI-rich systems.

Figure 2: Distribution on the sky (in horizontal coordinates) of our sample galaxies during a typical observation with the 30m telescope.The zenith is situated in the center of the figure.

ReferencesDownes,D & Solomon, P.M., 1998, ApJ, 507, 615 Giovanelli, R. et al., 2005, AJ, 130, 2598; Helfer, T.T., et al. 2003, ApJS, 145, 259;

Joergensen, I., Franx, M., Kjaergaard, P., 1996, MNRAS, 280, 167; Kauffmann, G., 1996, MNRAS, 281, 487; Kauffmann, G. et al., 2003,

MNRAS, 341, 54 Krumholz,M.R., McKee,C.F., Tumlinson,J.,2009a,ApJ, 693,216; Krumholz,M.R., McKee,C.F., Tumlinson,J.,2009a,ApJ,

699,865; Kuno, N. et al., 2007, PASJ, 59, 117; Leroy, A. et al 2009, AJ, 137, 4670; Mo, H.J., Mao, S., White, S.D.M., 1998, MNRAS,

295, 319; Obreschkow,D., Rawlings, S., 2009, ApJ, 696, L129

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Model results THINGS PILOT

Figure 4: Scaling relations between molecular gas fraction and stellar mass (left), molecular-to-atomic gas ratio and stellar surfacedensity (center), and atomic gas fraction and stellar surface density (right). The top panels show results for a compilation of nearbygalaxies from SDSS with HI data from the HyperLeda catalogue and CO data from the literature. We have done our best to ensurethat the CO measurements have been put on a common system with regard to conversion factor etc. In the bottom panel, we showthe same scaling relations for galaxies drawn from the THINGS/HERACLES survey (red) and from our pilot program (blue circlesdenote detections, and blue triangles denote upper limits). The grey points are from new galaxy formation models that include both themolecular and atomic gas phases (Jian Fu et al, in preparation). In the top panels, the scatter in quantities involving the molecular gasis huge. It is larger than predicted by the models and is inconsistent with our newer data. In contrast, the atomic gas scaling relationslook quite comparable to both the models and our more recent data. The limit in M(H2)/M∗ that we plan to reach with the proposedsurvey is plotted as a dashed line in the figure. As can be seen, the majority of the model galaxies lie above the line. The model galaxiesscattering below the line are gas-deficient for two main reasons: a) some are satellite galaxies in groups and clusters that have consumedmost of their gas, b) others are galaxies with small spin parameter that have not experienced a recent episode of gas accretion.

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Figure 5: 30m telescope aperture correction study for galaxies situated at the GASS redshift range (0.025 < z < 0.050). a) Relationbetween the optical diameter of the galaxy (D25) and the fraction of CO(1-0) line flux recovered at the center with the 22” beam of the30m telescope. Small points indicate the results from the simulated observations of a sample of 46 nearby spiral galaxies with high-qualityCO(1–0) maps (Kuno et al. 2007; Helfer et al. 2003) when they are placed at z=0.05 (red points), z=0.035 (green points), z=0.025 (bluepoints) and z=0.015 (grey points). A single central observation recovers most (> 70%) of the CO line flux in galaxies with D25 < 40”.The histogram indicates the optical size distribution of the GASS sample (the distribution of red galaxies is indicated in red). As can beseen, most of the largest galaxies are red and we do not expect to observe offsets for these. b) With an additional offset observation it ispossible to derive the fraction of CO(1-0) line flux detected at the center and from that estimate the total molecular gas mass in galaxieswith D25 > 40”. The offset is situated at a distance of 0.75Beam (∼ 16”) from the center of the galaxy in the direction of the opticalmajor axis. We tested different values of the separation and found 0.75 times the Beam to provide a reasonable compromise in terms ofour ability to probe the structure of the molecular gas, while still retaining enough intensity in the CO line in the offset position. Bigblack points in a) indicate the aperture corrections estimated for some of the sources of the pilot survey using this technique. c) CO linesare typically 0.3–0.4 times weaker in the offset position than in the center position for galaxies with D25 > 40”.

This source list comprises the 210 galaxies currently observed in HI by the GASS survey (GASS DR1).We will start our CO observations from this sample and incorporate new galaxies as soon as they areobserved in HI with Arecibo.

Extended source list (cont’d from cover page)

Source RA Dec LSR Velocity(J2000.0) (J2000.0) (km/s)

G9814 14:33:48.34 +03:57:24.7 0.02926G9863 14:47:25.16 +03:26:27.9 0.02736G10010 14:52:33.84 +03:08:40.6 0.02774G10019 14:51:53.39 +03:21:47.8 0.03077G10145 14:58:06.39 +04:06:03.6 0.04442G10218 15:11:40.36 +03:40:34.2 0.04637G11223 23:06:16.44 +13:58:56.3 0.03554G11298 23:13:30.40 +14:03:50.1 0.03943G11386 23:26:11.30 +14:01:48.1 0.04624G11956 00:08:20.77 +15:09:21.6 0.03951G11989 00:25:58.89 +13:55:45.9 0.04194G12371 11:13:06.41 +05:14:03.0 0.04318G12983 12:40:32.47 +05:21:20.0 0.04659G14831 10:05:30.27 +05:40:19.5 0.04439G15181 10:40:02.96 +06:01:14.1 0.04685G17640 10:59:29.95 +08:42:33.1 0.03486G18335 12:18:53.94 +10:00:10.2 0.04307G18469 12:32:51.50 +08:44:23.9 0.03378G18581 12:34:43.55 +09:00:16.9 0.04295G20144 09:35:02.02 +09:55:12.4 0.04961G20286 09:54:39.45 +09:26:40.7 0.03456G22999 10:23:16.42 +11:51:20.4 0.04547G23445 10:56:02.38 +11:52:19.9 0.04782G24741 12:17:50.81 +08:25:49.0 0.04921G24757 12:20:48.14 +08:42:14.4 0.04944G26822 12:51:29.07 +13:46:54.5 0.03756G26980 15:40:10.49 +06:04:27.8 0.04840G28143 12:37:11.40 +08:39:29.9 0.02826G28526 12:58:28.60 +11:25:35.3 0.04865G29842 11:21:31.76 +13:25:35.8 0.03408G30338 12:23:19.58 +14:18:13.5 0.04180G30401 12:34:45.20 +14:33:26.6 0.04648G31156 15:57:52.02 +04:15:44.3 0.02575G38703 14:50:29.40 +08:59:37.7 0.04014G38716 14:50:08.03 +09:04:45.9 0.04997G38718 14:50:09.96 +09:12:41.5 0.02907G38751 14:47:34.58 +09:13:51.7 0.02903G38752 14:47:59.39 +09:25:34.4 0.02875G38758 14:47:43.51 +09:32:17.4 0.02912G39567 15:27:47.43 +09:37:29.7 0.03119G39595 15:27:16.73 +10:02:40.3 0.04353G40024 13:33:38.21 +13:14:09.6 0.04319G40393 12:47:23.18 +08:17:32.6 0.04854G40494 12:57:04.50 +10:37:14.6 0.04628G40781 13:19:34.31 +10:27:17.5 0.04804G41969 15:15:31.55 +06:22:13.4 0.03508G41970 15:16:30.15 +06:14:08.7 0.04580G42015 15:12:01.77 +06:13:09.3 0.04619G42025 15:15:07.55 +07:01:16.5 0.03671G42141 15:16:19.14 +07:09:44.4 0.03603

Extended source list (cont’d from cover page)

Source RA Dec LSR Velocity(J2000.0) (J2000.0) (km/s)

G9384 14:15:09.84 +04:28:40.5 z=0.04908G9514 14:22:09.72 +04:31:16.1 0.02674G9572 14:35:35.75 +03:41:21.3 0.02796G9604 14:30:52.87 +03:16:08.3 0.03165G9619 14:28:33.31 +03:15:43.2 0.02772G9776 14:34:46.68 +03:20:29.7 0.02760G9814 14:33:48.34 +03:57:24.7 0.02926G57017 09:22:29.28 +14:27:43.4 z=0.03232G7509 14:30:19.95 +03:05:29.1 0.03122G13227 12:59:50.04 +05:02:51.2 0.04832G18421 12:20:06.48 +10:04:29.2 0.04337G24740 12:17:18.90 +08:43:32.7 0.04923G29487 15:57:54.57 +09:24:35.8 0.04280G38462 14:15:45.95 +10:26:19.9 0.02579G38748 14:48:59.37 +09:30:17.2 0.04666G38964 15:02:16.36 +11:55:03.3 0.03223G23315 10:42:00.75 +11:46:48.1 0.03295G9463 14:25:05.50 +03:13:59.3 0.03557G10132 14:58:05.71 +03:17:45.7 0.04427G11016 22:36:19.87 +14:18:52.3 0.03750G18279 12:20:23.11 +08:51:37.0 0.04881G40007 13:35:42.40 +13:19:51.3 0.04278G6565 12:49:38.20 +02:45:20.2 0.04765G6583 12:50:55.80 +03:11:49.3 0.04834G7050 13:49:09.69 +02:45:11.6 0.04889G7286 14:14:32.05 +03:11:24.9 0.02688G7457 14:27:13.78 +02:50:48.6 0.03567G7581 14:39:15.53 +02:43:40.9 0.02787G9507 14:20:32.84 +05:06:38.4 0.04961G9704 14:40:59.30 +03:08:13.5 0.02654G9748 14:39:17.95 +03:22:06.0 0.02794G9891 14:42:25.71 +03:13:55.0 0.02582G9917 14:40:25.99 +03:35:56.1 0.02815G10031 14:51:06.43 +04:50:32.6 0.02734G10040 14:52:35.22 +04:32:45.2 0.02859G10150 15:00:26.76 +04:10:44.5 0.03279G10292 15:13:22.09 +04:07:01.2 0.04260G10358 15:17:11.15 +03:21:05.8 0.03702G10367 15:15:53.86 +03:03:01.1 0.03793G10404 15:17:22.96 +04:12:48.9 0.03607G10447 15:18:40.93 +04:25:05.4 0.04714G10817 22:01:20.93 +12:11:48.1 0.02912G10884 22:14:30.63 +13:04:45.0 0.02574G12025 00:19:34.55 +16:12:15.1 0.03665G12455 11:20:17.80 +04:19:13.3 0.04910G12458 11:21:18.26 +03:39:53.1 0.03936G12460 11:20:48.31 +03:50:21.0 0.04942G12966 12:36:32.24 +06:10:10.5 0.03952G13037 12:43:14.97 +04:05:02.0 0.04855G13156 13:04:47.00 +03:54:17.8 0.04077G13549 13:45:25.31 +03:48:23.9 0.03245G14943 10:16:00.20 +06:15:05.2 0.04583G17659 10:58:07.60 +09:16:34.0 0.03444

Extended source list (cont’d from cover page)

Source RA Dec LSR Velocity(J2000.0) (J2000.0) (km/s)

G29090 14:38:10.21 +09:20:09.7 0.03029G29420 14:48:58.71 +12:29:24.5 0.04745G29699 11:08:18.34 +13:13:27.6 z=0.03401G30471 12:37:53.20 +14:16:52.7 0.02627G30479 12:37:08.07 +14:24:26.9 0.03075G30508 12:59:26.23 +14:20:30.1 0.04709G30811 14:18:45.69 +05:50:04.8 0.04891G38472 14:16:08.77 +10:35:43.9 0.02637G38529 14:09:46.82 +11:35:05.5 0.03818G38591 14:17:40.52 +10:34:60.0 0.02713G39448 15:20:37.22 +08:03:05.7 0.03381G39465 15:20:28.70 +08:17:06.6 0.03721G39467 15:19:53.53 +08:05:57.2 0.03343G39469 15:19:03.39 +08:08:19.4 0.03377G39605 15:25:59.84 +09:47:24.6 0.03391G39606 15:27:16.74 +09:46:03.8 0.04369G40247 13:59:42.62 +12:44:12.6 0.03917G40257 13:58:42.23 +13:27:22.9 0.03933G40317 13:55:33.72 +14:45:52.7 0.04083G40500 12:59:11.09 +10:30:06.0 0.04599G40570 13:11:04.94 +08:48:28.3 0.03253G40686 13:15:29.83 +09:51:00.6 0.04963G40790 13:19:44.64 +10:21:46.0 0.04886G41323 14:18:22.47 +08:05:51.0 0.04396G41482 14:31:52.89 +07:19:15.2 0.02727G41974 15:17:58.31 +06:44:45.4 0.03485G42017 15:15:24.85 +06:26:54.0 0.04524G42020 15:15:16.46 +06:39:18.5 0.03516G42140 15:15:31.97 +07:28:29.1 0.04572G42156 15:17:24.34 +07:29:21.9 0.03358G42175 15:18:32.43 +07:07:20.7 0.04560G9120 11:01:08.53 +05:02:06.1 0.03839G8695 10:23:06.49 +04:08:04.4 0.04845G27828 11:48:20.81 +06:20:42.4 0.03339G26854 12:55:23.78 +14:59:02.2 0.03530G16642 08:53:52.19 +05:14:53.4 0.02842G23194 10:33:33.43 +11:52:17.0 0.03404G10439 15:18:54.17 +04:06:36.0 0.03531G9554 14:27:29.62 +04:46:47.1 0.02755G39228 15:10:54.10 +08:25:04.1 0.04520G42063 15:07:42.49 +06:53:09.0 0.03074G38757 14:47:42.49 +09:39:34.0 0.02854G23745 11:34:48.95 +11:14:59.7 0.03587G8748 10:33:33.70 +04:15:49.8 0.02797G13097 12:55:07.74 +04:02:25.2 0.04823G41816 15:02:35.60 +07:53:35.9 0.04813G26740 08:28:12.32 +08:38:50.4 0.04418G40078 13:33:05.02 +14:12:18.5 0.04409G8724 10:22:31.19 +04:34:56.7 0.02857G57392 11:03:35.81 +15:51:08.5 0.04494G39570 15:26:22.19 +09:23:47.2 0.03235G40245 13:59:26.03 +12:47:18.5 0.03906G41063 13:49:23.66 +08:30:27.5 0.03790G42084 15:13:09.61 +07:51:53.1 0.04635G15241 10:50:47.21 +06:05:54.7 0.04199G29304 14:46:21.37 +13:01:15.5 0.04672G26959 15:47:15.59 +05:55:16.6 0.04189

Extended source list (cont’d from cover page)

Source RA Dec LSR Velocity(J2000.0) (J2000.0) (km/s)

G23584 11:11:37.87 +12:07:19.1 0.04216G39374 15:25:52.59 +07:49:10.6 0.03368G23187 10:33:53.37 +11:12:25.4 0.04984G42167 15:18:53.66 +07:34:33.3 0.03695G42402 15:51:25.22 +25:45:39.0 0.04597G47221 15:49:02.68 +17:56:25.6 0.03178G47405 15:59:28.63 +20:13:03.2 0.04914G18422 12:21:23.26 +09:50:53.0 0.04666G18900 10:20:01.62 +08:30:53.6 0.04531G21023 15:56:36.92 +27:29:12.0 0.04153G23408 10:53:22.37 +11:10:50.4 0.04302G23450 10:56:48.59 +12:05:35.7 0.04763G24094 12:20:30.18 +11:20:27.4 0.04307G25154 13:04:57.42 +12:04:44.6 0.03581G25214 13:12:32.82 +11:43:44.3 0.03110G25347 13:30:19.15 +11:30:42.5 0.03776G25575 14:06:06.72 +12:30:13.6 0.03792G26602 10:33:47.41 +12:43:58.2 0.03249G26958 15:46:54.34 +05:53:28.4 0.04188