The Identification of Physical Close Galaxy Pairs

Soares, Domingos

doi:10.1086/518240

Cited by 10 publications

(9 citation statements)

References 27 publications

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“…We follow Patton et al (2002) who suggest a projected separation of 20h −1 kpc and a difference in recessional velocities of 500km s −1 . Soares (2007) compares projected separation with spatial separation for a Monte Carlo simulated sample of gravitationally-bound pairs and finds that over 50% with projected separation ≤ 50kpc actually have spatial separation > 50kpc. Thus, we accept that projected separation is merely an approximation to spatial separation, and that the physical separation is likely to be higher.…”

Section: Pair Extraction and Cross-matchingmentioning

confidence: 99%

Star formation and AGN activity in interacting galaxies: a near-UV perspective

Scott¹,

Kaviraj²

2013

Monthly Notices of the Royal Astronomical Society

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We study nearby galaxies in close pairs to study the key factors affecting star formation and AGN activity triggered during galaxy interactions. Close pairs are selected from the Sloan Digital Sky Survey assuming a projected separation of <30kpc and recessional velocity difference <500km s −1 . Near-ultraviolet (NUV) fluxes from GALEX are used to estimate specific star formation rates (SSFRs). We find a factor of ∼5.3 increase in SSFR for low mass (10 8 -10 11 M ⊙ ) close pair galaxies and a factor of ∼2.1 increase in SSFR for high mass mass (10 11 -10 13 M ⊙ ) close pairs compared to the general galaxy population. Considering galaxies of all masses, we find a factor of ∼1.8 enhancement in SSFR for close pairs in field environments compared to non-pairs, with no significant increase for pairs in group and cluster environments. A modest decrease of a factor of ∼1.4 is found in the Seyfert fraction in close pair galaxies when compared to isolated galaxies, which suggests that mergers may not trigger AGN activity at the close-pair stage or may trigger a different class of AGN. This becomes a factor of ∼4.2 decrease when we restrict our analysis to high mass close pairs in group or cluster environments.

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Section: Pair Extraction and Cross-matchingmentioning

confidence: 99%

Star formation and AGN activity in interacting galaxies: a near-UV perspective

Scott¹,

Kaviraj²

2013

Monthly Notices of the Royal Astronomical Society

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“…More generally speaking, isolated associations of dwarf galaxies should be rare. They are known to exist (e.g., Tully et al 2006;Soares 2007), but their cosmological abundance and dependence on luminosity have not yet been adequately established (see Sales et al 2012, for a recent attempt).…”

Section: Introductionmentioning

confidence: 99%

Galaxy pairs in the Local Group

Fattahi

Navarro

Starkenburg

et al. 2013

Monthly Notices of the Royal Astronomical Society: Letters

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Current models of galaxy formation predict that galaxy pairs of comparable magnitudes should become increasingly rare with decreasing luminosity. This seems at odds with the relatively high frequency of pairings among dwarf galaxies in the Local Group. We use literature data to show that ∼ 30% of all satellites of the Milky Way and Andromeda galaxies brighter than M V = −8 are found in likely physical pairs of comparable luminosity. Besides the previously recognised pairings of the Magellanic Clouds and of NGC 147/NGC 185, other candidate pairs include the Ursa Minor and Draco dwarf spheroidals, as well as the And I/And III satellites of M31. These pairs are much closer than expected by chance if the radial and angular distributions of satellites were uncorrelated; in addition, they have very similar line-of-sight velocities and luminosities that differ by less than three magnitudes. In contrast, the same criteria pair fewer than 4% of satellites in N-body/semi-analytic models that match the radial distribution and luminosity function of Local Group satellites. If confirmed in studies of larger samples, the high frequency of dwarf galaxy pairings may provide interesting clues to the formation of faint galaxies in the current cosmological paradigm. 1 We define all virial quantities as those corresponding to a sphere of mean density equal to 200 times the critical density for closure. Furthermore, we shall hereafter refer to the stellar mass of a galaxy as "galaxy mass", for brevity.

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“…Using these empirical results to arrive at a true measure of the amount and timescales of triggered star formation is difficult. Pair samples are complex: they include some interlopers and are rich in galaxies in a variety of environments (e.g., Alonso et al 2006;Soares 2007). The progenitors of galaxy interactions come from a mixture of galaxy types (e.g., Focardi et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Isolating Triggered Star Formation

Barton

Arnold

Zentner

et al. 2007

ApJ

140

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Galaxy pairs provide a potentially powerful means of studying triggered star formation from galaxy interactions. We use a large cosmological N-body simulation coupled with a well-tested semi-analytic substructure model to demonstrate that the majority of galaxies in close pairs reside within cluster or group-size halos and therefore represent a biased population, poorly suited for direct comparison to ``field'' galaxies. Thus, the frequent observation that some types of galaxies in pairs have redder colors than ``field'' galaxies is primarily a selection effect. We select galaxy pairs that are isolated in their dark matter halos with respect to other massive subhalos (N=2 halos) and a control sample of isolated galaxies (N=1 halos) for comparison. We then apply these selection criteria to a volume-limited subset of the 2dF Galaxy Redshift Survey with M_Bj <= -19 and obtain the first clean measure of the typical fraction of galaxies affected by triggered star formation and the average elevation in the star formation rate. We find that 24% (30.5%) of these L^\star and sub-L^{\star} galaxies in isolated 50 (30) kpc/h pairs exhibit star formation that is boosted by a factor of >~ 5 above their average past value, while only 10% of isolated galaxies in the control sample show this level of enhancement. Thus, 14% (20 %) of the galaxies in these close pairs show clear triggered star formation. The isolation criteria we develop provide a means to constrain star formation and feedback prescriptions in hydrodynamic simulations and a very general method of understanding the importance of triggered star formation in a cosmological context. (Abridged.)Comment: 12 pages, 10 figures, emulateapj format, accepted by Ap

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The Identification of Physical Close Galaxy Pairs

Cited by 10 publications

References 27 publications

Star formation and AGN activity in interacting galaxies: a near-UV perspective

Star formation and AGN activity in interacting galaxies: a near-UV perspective

Galaxy pairs in the Local Group

Isolating Triggered Star Formation

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