Hot gas in galaxy pairs

Olga Melnyk

It is known that the dark matter is concentrated in individual haloes of galaxies and is located in the volume of clusters.

Groups of galaxies are the intermediate link between individual galaxies and galaxy clusters.It is not known for small galaxy groups, how the dark matter is distributed: in a single group halo or in separate galaxy haloes???

Idea

HCG 79,Seyfert’s Sextet

dada Rocha andRocha andM. de OliveiraM. de Oliveira((20052005, 2008), 2008)

M/L=6.2 M/L

HCG 95

M/L=31.2 M/L

HCG 88HCG 15

Jeltema et al. (2008) used Chandra observations of 13 nearby groups of galaxies to investigate the hot gas content of their member galaxies. They found that a large fraction of near-IR bright, early-type galaxies in groups have extended X-ray emission, indicating that they retain significant hot gas halos even in these dense environments.

Gastaldello et al. 2006presented radial mass profiles for 16 relaxed

galaxy groups-poor clusters (kT~ 1-3 keV) selected from the Chandra and XMM data archives.After accounting for the mass of hot gas, the resulting mass profiles are described well by a two-component model consisting of dark matter (DM), represented by an NFW model, and stars from the central galaxy.

What is the group dark matter halo in the case of equal mass galaxies?

Main goal of our work

To find where located dark matter in loose galaxy groups: in haloes of individual galaxies or in the volume of the system

and to find the scale on which individual halo

transform into group's halo

The observed baryonic masses of groups are a small fraction of the X-ray determined masses, which implies that groups

are dominated by dark matter (Mulchaey, 2000).

In the case of individual galactic halos, the X-ray emission should be concentrated toward the galaxies and the extended source should exhibit a few-component structure.

If the group has a common corona, its X-ray

emission should be concentrated toward the center of mass of the system and not toward the individual galaxies.

A choice between these two models can be made

based on X-ray observations of galaxy groups (idea of Dolgachev et al., 2002 in case of galaxy triplets).

What we need for analysis?

• Sample of galaxy groups (archived observations of XMM-Newton data)

• Model of dark matter distribution

X-ray emission from galaxies in groups

Diffuse X-ray emission from spiral dominant groups is usually much fainter than elliptical dominant groups. Whereas the bulk of ISM in spiral galaxies is in the form of HI and H2, the ISM ellipticals consists primarily of hot (T > 106 K) plasma. This plasma produces X-rays by combination of thermal bremsstrahlung, radiative recombination, and line emission from highly ionized trace elements.

We need the presence of early-type galaxies in our sample!

Early-type galaxies (E and S0)

LX/LB

X-ray bright X-ray faint

Thermal emission from interstellar gas at temperature kT~1 keV

-Soft thermal component with kT~0.3 keV- hard component (thermal bremsstrahlung with kT>5 keV or power law), it origin is low-mass binaries (LMXBs)

field galaxiescluster/group galaxies

There are two main sources of hot gas in elliptical galaxies: internal and external:

Evolving stars inside the elliptical galaxy continuously eject gas that is raised the stellar kinematic temperature to 1 keV (107 K). Type Ia supernovae provide some additional heating. The large X-ray luminosities of massive E galaxies, Lx ~1040−1043 ergs s−1, indicate that most of the internally produced gas is currently trapped in the galactic or group potential. But at early times, when most of the galactic stars were forming, Type II supernovae were frequent enough to drive winds of enriched gas into the local environment.

Gas expelled in this manner from both central and non-central group or clustergalaxies has enriched the hot gas far beyond the stellar image of the central luminous E or cD galaxy.

In time, some of this local (circumgalactic) gas flows back into the central galaxy, providing an external source of gas. Continued accretion from the ambient cosmological flow that is gravitationally bound to the group or cluster is an additional source of external gas.

Our sample

We focus on ~equal mass galaxy pairs. These small populated groups represent

most common case of group.

• Karachentsev (1987) Catalog of isolated galaxy pairs (Northern catalog). • Vorontsov-Veliaminov catalog of interacting galaxies (1958-2000)• Original papers

We have found archived XMM data for 5 galaxy pairs

SDSS 2MASS

NGC3607+NGC3608 = KPG278 (E+E pair)ΔV = 190 km/s, <V>=1030 km/sd=5.9’ - 24 kpc

sclmin=indef sclmin=3 sclmin=5

sclmin=10

smoothed X-ray images with sigmamin=3 and different kernel size, 0.3-8 keV

NGC3607+NGC3608 = KPG278 (E+E pair)DSS image with X-ray contours

0.3-8 keV

NGC4065+NGC4061 = VV179 (E+E pair???)ΔV=877 km/s

Abell 299

NGC4066+NGC4070 (E+E pair)ΔV=152 km/s

smoothed X-ray images with different sigmamin and kernel size, 0.3-8 keV

NGC4065+NGC4061 (VV179) and NGC4066+NGC4070 DSS image with X-ray contours

0.3-8 keV

Red DSS image

Abell194

KPG032VV963ARP308

NGC545 v=5338 km/sNGC547 v=5468 km/sNGC541 v=5422 km/s

ΔVp=130 km/s

smoothed X-ray images with t sigmamin=3 and differenkernel size, 0.3-8 keV

NGC545+NGC547 and NGC541 DSS image with X-ray contours

0.3-8 keV

KTG50 DSS image with X-ray contours

0.3-8 keV

Our model assumptions:

• halo of each galaxy is assumed to be spherically symmetric and to be in hydrostatic equilibrium:

2

)(1

r

rGM

dr

d

dr

dP

g

• total density:

cr

rx

• T = const

• I ~ ρg2

20

1)(

xxx

NFW

drrrrMr

0

24)(

rc1=rc2=1kpc, M1=M2=1011M

d=15 kpc, kT=1keV

rc1=rc2=0.2 kpc, M1=M2=1011M

d=15 kpc, kT=1keV

rc1=rc2=4 kpc, M1=M2=1011M

d=15 kpc, kT=1keV

rc1=rc2=1 kpc, M1=1011M, M2=2x1011M

d=15 kpc, kT=1keV

rc1=rc2=1kpc, M1=M2=1011M

d=5 kpc, kT=1keV

The steps of analysis1. To determine the temperature.2. To construct the galaxies’ profiles in opposite

direction relative to neighboring galaxies. 3. We will consider the galaxies as separate and fit

parameters of characteristic radius of dark matter halo rc and mass of galaxy М in such a way that our model profile coincides in the best way with observational profile.

4. To use obtained values of rc1, rc2, M1, M2 for haloes of each galaxy and simulate the pair.

5. To reconstruct the profile crossing galaxy centers and to compare results with observations.

6. To make conclusions about presence common or separate haloes of our galaxy pairs.

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