A new population of recently quenched elliptical galaxies in the SDSS

McIntosh, Daniel H.; Wagner, Cory R.; Cooper, Andrew P.; Bell, Eric F.; Kereš, Dušan; Bosch, Frank C. van den; Gallazzi, Anna; Haines, Tim; Mann, Justin L.; Pasquali, A.; Christian, Allison M.

doi:10.1093/mnras/stu808

Cited by 54 publications

(85 citation statements)

References 234 publications

(278 reference statements)

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“…The evolution and assembly of ellipticals is well-understood to be heterogeneous after z∼0.6 . Ellipticals that are blue and post-starburst have been found in local clusters, in a phase assumed to last 0.5 Gyr, consistent with our recent star formation event (McIntosh et al 2014). The formation of these galaxies can be explained with minor mergers, which is consistent with our imaging indicating all of the blue ellipticals have either companions or tidal debris.…”

Section: Resultssupporting

confidence: 90%

Star Formation in the Cluster Merger DLSCL J0916.2+2953

Mansheim

Lemaux

Dawson

et al. 2017

ApJ

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We investigate star formation in DLSCL J0916.2+2953, a dissociative merger of two clusters at z=0.53 that has progressed 1.1 +1.3 −0.4 Gyr since first pass-through. We attempt to reveal the effects a collision may have had on the evolution of the cluster galaxies by tracing their star formation history. We probe current and recent activity to identify a possible star formation event at the time of the merger using EW(Hδ), EW([OII]), and D n (4000) measured from the composite spectra of 64 cluster and 153 coeval field galaxies. We supplement Keck DEIMOS spectra with DLS and HST imaging to determine the color, stellar mass, and morphology of each galaxy and conduct a comprehensive study of the populations in this complex structure. Spectral results indicate the average cluster and cluster red sequence galaxies experienced no enhanced star formation relative to the surrounding field during the merger, ruling out a predominantly merger-quenched population. We find that the average blue galaxy in the North cluster is currently active and in the South cluster is currently post-starburst having undergone a recent star formation event. While the North activity could be latent or longterm merger effects, a young blue stellar population and irregular geometry suggest the cluster was still forming prior the collision. While the South activity coincides with the time of the merger, the blue early-type population could be a result of secular cluster processes. The evidence suggests that the dearth or surfeit of activity is indiscernible from normal cluster galaxy evolution.

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Section: Resultssupporting

confidence: 90%

Star Formation in the Cluster Merger DLSCL J0916.2+2953

Mansheim

Lemaux

Dawson

et al. 2017

ApJ

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“…Consistent with the merger origin, past observational studies of morphology and kinematics of K+A galaxies in the field hint that they are merger remnants on the way to becoming early-type galaxies (Norton et al 2001;Quintero et al 2004;Goto 2007;McIntosh et al 2014). As such, they display both early-type morphologies and signs of interactions (Schweizer 1982;Zabludoff et al 1996;Quintero et al 2004;Balogh et al 2005;Yang et al 2008;Pracy et al 2009).…”

Section: Introductionmentioning

confidence: 77%

From Starburst to Quiescence: Testing Active Galactic Nucleus Feedback in Rapidly Quenching Post-Starburst Galaxies

Yesuf

Faber

Trump

et al. 2014

ApJ

120

151

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Post-starbursts are galaxies in transition from the blue cloud to the red sequence. Although they are rare today, integrated over time they may be an important pathway to the red sequence. This work uses Sloan Digital Sky Survey, the Galaxy Evolution Explorer, and Wide-field Infrared Survey Explorer observations to identify the evolutionary sequence from starbursts to fully quenched post-starbursts (QPSBs) in the narrow mass range log M(M ) = 10.3-10.7, and identifies "transiting" post-starbursts (TPSBs) which are intermediate between these two populations. In this mass range, ∼0.3% of galaxies are starbursts, ∼0.1% are QPSBs, and ∼0.5% are the transiting types in between. The TPSBs have stellar properties that are predicted for fast-quenching starbursts and morphological characteristics that are already typical of early-type galaxies. The active galactic nucleus (AGN) fraction, as estimated from optical line ratios, of these post-starbursts is about three times higher ( 36% ± 8%) than that of normal star forming galaxies of the same mass, but there is a significant delay between the starburst phase and the peak of nuclear optical AGN activity (median age difference of 200 ± 100 Myr), in agreement with previous studies. The time delay is inferred by comparing the broadband near-NUV-to-optical photometry with stellar population synthesis models. We also find that starbursts and post-starbursts are significantly more dust obscured than normal star forming galaxies in the same mass range. About 20% of the starbursts and 15% of the TPSBs can be classified as "dust-obscured galaxies" (DOGs), with a near-UV-to-mid-IR flux ratio of 900, while only 0.8% of normal galaxies are DOGs. The time delay between the starburst phase and AGN activity suggests that AGNs do not play a primary role in the original quenching of starbursts but may be responsible for quenching later low-level star formation by removing gas and dust during the post-starburst phase.

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“…The position of star-forming blue ETGs on the colour-magnitude/colour-stellar mass diagrams has been interpreted as possible migration from the red sequence to the blue cloud after acquiring sufficient fuel for star formation or fading post-starburst galaxies (Kannappan et al 2009;Huertas-Company et al 2010;Thilker et al 2010;Marino et al 2011;Moffett et al 2012;McIntosh et al 2014;Rutkowski et al 2014;Moffett et al 2015;Wong et al 2015). The sample of a few blue ETGs from other studies was found to host a significant amount of molecular gas (∼ 10 7−9 M⊙) with a linear dependence on star formation surface density within the galaxy and a higher molecular gas star formation efficiency than in normal star-forming late-type galaxies (Wei et al 2010;Stark et al 2013).…”

Section: Discussionmentioning

confidence: 99%

Structural analysis of star-forming blue early-type galaxies

George

2017

A&A

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Context. Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L * elliptical galaxies in the local Universe. Aims. We wish to understand the reason for star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. Methods. We carried out structural analysis on SDSS r-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural parameters, analysed the residuals from best-fit to surface brightness distribution, and constructed the galaxy scaling relations. Results. We found that star-forming blue early-type galaxies are bulge-dominated systems with axial ratio > 0.5 and surface brightness profiles fitted by Sersic profiles with index (n) mostly > 2. Twenty-three galaxies are found to have n < 2; these could be hosting a disc component. The residual images of the 32 galaxy surface brightness profile fits show structural features indicative of recent interactions. The star-forming blue elliptical galaxies follow the Kormendy relation and show the characteristics of normal elliptical galaxies as far as structural analysis is concerned. There is a general trend for high-luminosity galaxies to display interaction signatures and high star formation rates. Conclusions. The star-forming population of blue early-type galaxies at low redshifts could be normal ellipticals that might have undergone a recent gas-rich minor merger event. The star formation in these galaxies will shut down once the recently acquired fuel is consumed, following which the galaxy will evolve to a normal early-type galaxy.

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A new population of recently quenched elliptical galaxies in the SDSS

Cited by 54 publications

References 234 publications

Star Formation in the Cluster Merger DLSCL J0916.2+2953

Star Formation in the Cluster Merger DLSCL J0916.2+2953

From Starburst to Quiescence: Testing Active Galactic Nucleus Feedback in Rapidly Quenching Post-Starburst Galaxies

Structural analysis of star-forming blue early-type galaxies

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