New Techniques for Relating Dynamically Close Galaxy Pairs to Merger and Accretion Rates: Application to the Second Southern Sky Redshift Survey

Abstract

The galaxy merger and accretion rates, and their evolution with time, provide important tests for models of galaxy formation and evolution. Close pairs of galaxies are the best available means of measuring redshift evolution in these quantities. In this study, we introduce two new pair statistics, which relate close pairs to the merger and accretion rates. We demonstrate the importance of correcting these (and other) pair statistics for selection e †ects related to sample depth and completeness. In particular, we highlight the severe bias that can result from the use of a Ñux-limited survey. The Ðrst statistic, gives N c , the number of companions per galaxy within a speciÐed range in absolute magnitude.is directly N c related to the galaxy merger rate. The second statistic, gives the total luminosity in companions, per L c , galaxy. This quantity can be used to investigate the mass accretion rate. Both and are related to N c L c the galaxy correlation function m and luminosity function /(M) in a straightforward manner. Both statistics have been designed with selection e †ects in mind. We outline techniques that account for various selection e †ects and demonstrate the success of this approach using Monte Carlo simulations. If one assumes that clustering is independent of luminosity (which is appropriate for reasonable ranges in luminosity), then these statistics may be applied to Ñux-limited surveys. These techniques are applied to a sample of 5426 galaxies in the Second Southern Sky Redshift Survey (SSRS2). This is the Ðrst large, well-deÐned low-z survey to be used for pair statistics. Using close (5 h~1 h~1 kpc) kpc ¹ r p ¹ 20 dynamical (*v ¹ 500 km s~1) pairs, we Ðnd andat z \ 0.015. These are the Ðrst secure estimates of low-L _ redshift pair statistics, and they will provide local benchmarks for ongoing and future pair studies. If N c remains Ðxed with redshift, simple assumptions imply that D6.6% of present day galaxies with have undergone mergers since z \ 1. When applied to redshift surveys of more [21 ¹ M B ¹ [18 distant galaxies, these techniques will yield the Ðrst robust estimates of evolution in the galaxy merger and accretion rates.

Galaxy and Mass Assembly (GAMA): merging galaxies and their properties

“…Following Patton et al (2000Patton et al ( , 2002 and our previous work, the number of close companions per galaxy is:…”

“…The second weight is for galaxies close (within 500 km s −1 ) to the redshift limits of each volume-limited box, and accounts for possible companions missed because they lie just beyond these boundaries. As in Patton et al (2000Patton et al ( , 2002) the value of this weight is set at 2. Similar weights need to be applied to the primary sample as well, to account for missed primaries in the same manner (recall that both primary and secondary samples are the same):…”

“…With the availability of large redshift databases from giant redshift surveys it is now possible to identify close pairs in 3D space (position and relative velocity), such that, if bound, these galaxies will merge within the dynamical friction timescale (≈ 1 Gyr). The formalism and its application to the SSRS2 and CFRS surveys have been presented in Patton et al (2000Patton et al ( , 2002; we have used this method to measure the local pair fraction and merger rate from the Millennium Galaxy Catalogue (MGC; Liske et al 2003;Driver et al 2005) in De Propris et al ( , 2007, where we also compared the results to asymmetrybased estimates (De Propris et al 2007). Several other studies have searched for dynamically close pairs out to z ∼ 1 (e.g.…”

The SAMI Galaxy Survey: spatially resolving the environmental quenching of star formation in GAMA galaxies

“…Owers et al 2012), while galaxy merger or interaction rates can be studied using analysis of galaxy close pairs (e.g. Patton et al 2000;Robotham et al 2014). …”

GRB 080517: a local, low-luminosity gamma-ray burst in a dusty galaxy at z = 0.09

“…Those authors recognise however that this cutoff requires a trade-off between contamination and completeness, with genuine pairs observed out to ∆v ∼ 600 km s −1 separations (Ellison et al 2008;Patton et al 2000). Ellison et al (2008) identified an enhancement in star formation rate for pairs with projected separations < 30 − 40 kpc, a criterion easily satisifed by the companion in this case (16 ′′ represents ∼ 27 kpc at this redshift), suggesting that the star formation observed in both host and companion is likely influenced by their proximity.…”