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Register a new userFrom Starburst to Quiescence: Testing AGN feedback in Rapidly Quenching Post-Starburst Galaxies
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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 SDSS, GALEX, and WISE observations to identify the evolutionary sequence from starbursts to fully quenched post-starbursts in the narrow mass range $log M(M_odot) = 10.3-10.7$, and identifies transiting post-starbursts which are intermediate between these two populations. In this mass range, $sim 0.3%$ of galaxies are starbursts, $sim 0.1%$ are quenched post-starbursts, and $sim 0.5%$ are the transiting types in between. The transiting post-starbursts have stellar properties that are predicted for fast-quenching starbursts and morphological characteristics that are already typical of early-type galaxies. The AGN fraction, as estimated from optical line ratios, of these post-starbursts is about 3 times higher ($gtrsim 36 pm 8 %$) 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 $gtrsim 200 pm 100$ Myr), in agreement with previous studies. The time delay is inferred by comparing the broad-band 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 transiting post-starbursts can be classified as the Dust-Obscured Galaxies (DOGs), while only $0.8%$ of normal galaxies are DOGs.The time delay between the starburst phase and AGN activity suggests that AGN do not play a primary role in the original quenching of starbursts but may be responsible for quenching later low-level star formation during the post-starburst phase.
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We present the first study of the large-scale clustering of post-starburst (PSB) galaxies in the high redshift Universe ($0.5<z<3.0$). We select $sim4000$ PSB galaxies photometrically, the largest high-redshift sample of this kind, from two deep large-scale near-infrared surveys: the UKIDSS Ultra Deep Survey (UDS) DR11 and the Cosmic Evolution Survey (COSMOS). Using angular cross-correlation techniques, we estimate the halo masses for this large sample of PSB galaxies and compare them with quiescent and star-forming galaxies selected in the same fields. We find that low-mass, low-redshift ($0.5<z<1.0$) PSB galaxies preferentially reside in very high-mass dark matter halos (M$_{text{halo}}>10^{14}$M$_{odot}$), suggesting they are likely to be infalling satellite galaxies in cluster-like environments. High-mass PSB galaxies are more weakly clustered at low redshifts, but they reside in higher mass haloes with increasing look-back time, suggesting strong redshift-dependent halo downsizing. These key results are consistent with previous results suggesting that two main channels are responsible for the rapid quenching of galaxies. While high-redshift ($z>1$) galaxies appear to be quenched by secular feedback mechanisms, processes associated with dense environments are likely to be the key driver of rapid quenching in the low-redshift Universe ($z<1$). Finally, we show that the clustering of photometrically selected PSBs are consistent with them being direct descendants of highly dust-enshrouded sub-millimetre galaxies (SMGs), providing tantalising evidence for the oft-speculated evolutionary pathway from starburst to quiescence.
We investigate radio-mode AGN activity among post-starburst galaxies from the Sloan Digital Sky Survey to determine whether AGN feedback may be responsible for the cessation of star formation. Based on radio morphology and radio-loudness from the FIRST and NVSS data, we separate objects with radio activity due to an AGN from ongoing residual star formation. Of 513 SDSS galaxies with strong A-star spectra, 12 objects have 21-cm flux density above 1 mJy. These galaxies do not show optical AGN emission lines. Considering that the lifetime of radio emission is much shorter than the typical time-scale of the spectroscopic features of post-starburst galaxies, we conclude that the radio-emitting AGN activity in these objects was triggered after the end of the recent starburst, and thus cannot be an important feedback process to explain the post-starburst phase. The radio luminosities show a positive correlation with total galaxy stellar mass, but not with the mass of recently formed stars. Thus the mechanical power of AGN feedback derived from the radio luminosity is related to old stellar populations dominating the stellar mass, which in turn are related to the masses of central supermassive black holes.
We consider the morphology, stellar populations, structure and AGN activity of 10 post-starburst (K+A) galaxies with HST observations, full spectral coverage in the optical, spectral energy distributions from 0.2 to 160 $mu$m, X-ray and radio data. Our results show that the PSG phenomenon is related to mergers and interactions, and that star formation was likely triggered during close passes prior to final coalescence. We performed a detailed qualitative analysis of the observed light distribution, including low-surface brightness tidal features and color profiles, in high-resolution multi-band imaging with HST. We find evidence that star formation was centrally concentrated and that quenching took place from the inside-out, consistent with the occurrence of a feedback episode. Most of our PSGs contain massive bulges and therefore should host supermassive black holes. We search for AGN activity in spectra (line ratios), optical variability, X-ray emission at 0.5--7.0 KeV and radio emission at 20cm: all four lines of evidence show there is no active AGN accreting at more than 0.1% of the Eddington luminosity. We conclude that mergers may be a necessary, but not a sufficient condition, for AGN activity and that they are not likely to be important in our objects. If PSGs are good test cases for quenching and evolution to the red sequence, AGNs may play a smaller role than expected.
Post starburst E+A galaxies are thought to have experienced a significant starburst that was quenched abruptly. Their disturbed, bulge-dominated morphologies suggest that they are merger remnants. We present ESI/Keck observations of SDSS J132401.63+454620.6, a post starburst galaxy at redshift z = 0.125, with a starburst that started 400 Myr ago, and other properties, like star formation rate (SFR) consistent with what is measured in ultra luminous infrared galaxies (ULRIGs). The galaxy shows both zero velocity narrow lines, and blueshifted broader Balmer and forbidden emission lines (FWHM=1350 +- 240 km/s). The narrow component is consistent with LINER-like emission, and the broader component with Seyfert-like emission, both photoionized by an active galactic nucleus (AGN) whose properties we measure and model. The velocity dispersion of the broad component exceeds the escape velocity, and we estimate the mass outflow rate to be in the range 4-120 Mo/yr. This is the first reported case of AGN-driven outflows, traced by ionized gas, in post starburst E+A galaxies. We show, by ways of a simple model, that the observed AGN-driven winds can consistently evolve a ULIRG into the observed galaxy. Our findings reinforce the evolutionary scenario where the more massive ULIRGs are quenched by negative AGN feedback, evolve first to post starburst galaxies, and later become typical red and dead ellipticals.
We present the evolution in the number density and stellar mass functions of photometrically selected post-starburst galaxies in the UKIDSS Deep Survey (UDS), with redshifts of 0.5<z<2 and stellar masses logM>10. We find that this transitionary species of galaxy is rare at all redshifts, contributing ~5% of the total population at z~2, to <1% by z~0.5. By comparing the mass functions of quiescent galaxies to post-starburst galaxies at three cosmic epochs, we show that rapid quenching of star formation can account for 100% of quiescent galaxy formation, if the post-starburst spectral features are visible for ~250Myr. The flattening of the low mass end of the quiescent galaxy stellar mass function seen at z~1 can be entirely explained by the addition of rapidly quenched galaxies. Only if a significant fraction of post-starburst galaxies have features that are visible for longer than 250Myr, or they acquire new gas and return to the star-forming sequence, can there be significant growth of the red sequence from a slower quenching route. The shape of the mass function of these transitory post-starburst galaxies resembles that of quiescent galaxies at z~2, with a preferred stellar mass of logM~10.6, but evolves steadily to resemble that of star-forming galaxies at z<1. This leads us to propose a dual origin for post-starburst galaxies: (1) at z>2 they are exclusively massive galaxies that have formed the bulk of their stars during a rapid assembly period, followed by complete quenching of further star formation, (2) at z<1 they are caused by the rapid quenching of gas-rich star-forming galaxies, independent of stellar mass, possibly due to environment and/or gas-rich major mergers.
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