Renato FalomoINAF – Observatory of Padova, Italy

A. Treves and E.P. Farina Insubria University , Como, Italy

Interacting Galaxies and Binary Quasars: A Cosmic Rendezvous

(IPCT - Trieste – April 2012)

• Search for low redshift QSO pairs • Dynamical study of QSO pairs • Masses of the (bound) pairs

Renato Falomo 1

Properties of low redshift QSO pairs

Simple statistics of quasars

Renato Falomo 2

• Rare objects ( space density: 10-6 Mpc-3 dm-1) [ also depends on the redshift]

• In the most recent catalogues 105 spectroscopic QSOs

• Main contributions: 2dF & SDSS

• > 1 order of mag more photometric QSOs

Search for low redshift QSO pairs

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SDSS (DR7)

• Projected separation < 500 kpc• V < 500 km/s (from catalogue)• Redshift: < 0.8 ( [OIII] in the spectra )

Low redshift QSO can be studied easily and with greater details

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Sample of low redshift QSO pairs

6 QSO pairs found that satisfy the criteria

Farina, Falomo, Treves 2011 , MNRAS

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Estimation of the systemic velocity difference

Homogeneous measurements of the centroid from [OIII] emission lines.

VR accuracy 10-30 km/s

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The (minimum) Virial mass of the systems

M(min) from V and the projected separation

Average projection factor : <C> = 3.4

Mvir ≈ 3.4 x Mvir(min)

Mass is larger than that expected from that of the host galaxies

The host galaxies of QSO

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QSO are hosted in luminous massive bulge dominated galaxies

Decarli, Falomo, Treves et al 2009 MNRAS 402 2453

Host Luminosity (M*-1) < M < (M*-2)

Kotilainen, Falomo, Decarli, et al 2009, ApJ 703 1663Decarli, Falomo, Treves, et al 2009 MNRAS 402 2453

Falomo, et al 2008 ApJ 673 694

Cosmic evolution of RLQ hosts up to z ~ 3VLT+AO

M*

M*-1

M*-2

Falomo, et al 2008 ApJ 673 694

The stellar mass of the systems

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From galaxy luminosity to stellar masses

Decarli, Falomo, Treves et al 2009 MNRAS 402 2453

Host Luminosity (M*-1) < M < (M*-2)

Host galaxy mass 1011 - 1012 Msun

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Virial mass vs stellar mass of QSO pairs

• Virial mass consistent with host galaxy masses

• Virial mass greater than the stellar mass (2

cases)

Why virial mass is so big ?

• Not bound system (possible for individuals but unlikely)• QSO are in a cluster of galaxies• Additional (unseen) mass in the system

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QSO PAIRS – GALAXY ENVIRONMENTSSearch for excess of galaxies around the QSO pairs

SDSS images ( mag limit 21.3) M*+1 (at z = 0.5)

Study the galaxy counts around the QSO pairs

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QSO PAIRS – GALAXY ENVIRONMENTS

Results for 6 low redshift QSO pairs

• Only in one case we find a significant overdensity of galaxies.

• In the other 5 QSO pairs the environment is poor (no significant overdensity of galaxies is found )

• No galaxy cluster found for QSO pairs with high

Virial Mass

The missing mass in QSO pairs

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Log(Mcl) [1012 Msun]

Some bound systems

require

M/L > 50-100

Estimate the M/L ratio of the system from Mvirand observed galaxy overdensity (or limits).

Farina, Falomo, Treves 2011 , MNRAS

Summary & Conclusions

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• Dynamical study of 6 redshift QSO pairs confirm they are bound systems.

• QSO pairs live in poor environments ( similar to normal QSO )

• Comparison between Virial mass and host galaxy stellar mass show different behavior and suggests the presence (in some cases) of an extended massive halo (cold gas or dark matter ?) SEE also next talk by E.P. Farina CAVEATS & Future Obs.

• sample is SMALL • need to extend the study to more QSO pairs to firmly assess the dynamical behavior of pairs• this may require to probe higher redshift QSO pairs and thus NIR spectroscopy to observe [OIII ] lines