A large sample of Kohonen selected E+A (post-starburst) galaxies from the Sloan Digital Sky Survey

Abstract

Context. The galaxy population in the contemporary Universe is characterised by a clear bimodality, blue galaxies with significant ongoing star formation and red galaxies with only a little. The migration between the blue and the red cloud of galaxies is an issue of active research. Post starburst (PSB) galaxies are thought to be observed in the short-lived transition phase. Aims. We aim to create a large sample of local PSB galaxies from the Sloan Digital Sky Survey (SDSS). Another aim is to present a tool set for an efficient search in a large database of SDSS spectra based on Kohonen self-organising maps (SOMs). Methods. We computed a huge Kohonen SOM for ∼ 10 6 spectra from SDSS Data Release 7. The SOM is made fully available, in combination with an interactive user interface, for the astronomical community. We selected a large sample of PSB galaxies taking advantage of the clustering behaviour of the SOM. The morphologies were inspected on deep co-added SDSS images. We used the Portsmouth galaxy property computations to study the evolutionary stage of the PSB galaxies and archival multi-wavelength data to search for hidden AGNs. Results. We compiled a catalogue of 2 665 PSB galaxies with redshifts z < 0.4. In the colour-mass diagram, the PSB sample is clearly concentrated towards the region between the red and the blue cloud. The relative frequency of distorted PSB galaxies is at least 57% for EW(Hδ)> 5Å , significantly higher than in the comparison sample. The search for AGNs based on conventional selection criteria in the radio and MIR results in a low AGN fraction of ∼ 2 − 3%. We confirm an MIR excess in the mean SED of the E+A sample that may indicate hidden AGNs, though other sources are also possible.

Enhanced atomic gas fractions in recently merged galaxies: quenching is not a result of post-merger gas exhaustion

“…Regarding gas consumption, several studies have shown that post-starburst galaxies retain a considerable molecular (French et al 2015;Rowlands et al 2015;Alatalo et al 2016;Suess et al 2017;Smercina et al 2018) and atomic (Buyle et al 2006;Zwaan et al 2013) gas reservoirs. Since a significant fraction of post-starbursts seem to be related to late stage mergers (Zabludoff et al 1996;Goto 2005;Meusinger et al 2017;Pawlik et al 2018) their substantial gas reservoirs indicate that the gas remains even after an interactioninduced starburst is complete. Finally, since 40 per cent of earlytype galaxies have been shown to maintain significant molecular gas reservoirs (e.g.…”

Welcome to the Twilight Zone: The Mid-infrared Properties of Post-starburst Galaxies

“…Though all of these studies could be pointing to low-luminosity AGNs being present, none are definitive. Meusinger et al (2017) studied a large sample of E+A galaxies, finding a slightly elevated number of luminous (> 10 23 W) 1.4 GHz continuum sources and enhanced fraction of mid-IR WISE selected (Assef et al 2013) AGNs, and confirmed the rising mid-IR SED discussed by Melnick & De Propris (2013), but concluded while E+A galaxies do not host strong AGNs, they may contain obscured and/or low-luminosity AGNs or require significant emission from post-AGB stars (as discussed in §3.2.2).…”

The IAC Stripe82 Legacy Survey: Improved Sky-rectified Images

“…Amid this new set of deep imaging surveys, the IAC Stripe 82 Legacy Survey is playing a significant role (see e.g. Meusinger et al 2017;Trujillo et al 2017; Román & Trujillo 2017a,b;Peters et al 2017).The IAC Stripe 82 Legacy Survey is a new co-addition of the SDSS Stripe 82 data (Abazajian et al 2009), especially reduced to preserve the faintest surface brightness features of this data set. The survey maps a 2.5 degree wide stripe along the Celestial Equator in the Southern Galactic Cap (-50 • < R.A. < 60 • , -1.25 • < Dec.< 1.25 • ) with a total of 275 square degrees in all the five SDSS filters (u,g,r,i,z).…”

“…Amid this new set of deep imaging surveys, the IAC Stripe 82 Legacy Survey is playing a significant role (see e.g. Meusinger et al 2017;Trujillo et al 2017; Román & Trujillo 2017a,b;Peters et al 2017).…”