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MAPPING THE POLARIZATION OF THE RADIO-LOUD Ly<i>α</i>NEBULA B3 J2330+3927
You, Chang,Zabludoff, Ann,Smith, Paul,Yang, Yujin,Kim, Eunchong,Jannuzi, Buell,Prescott, Moire K. M.,Matsuda, Yuichi,Lee, Myung Gyoon American Astronomical Society 2017 The Astrophysical journal Vol.834 No.2
<P>Ly alpha nebulae, or 'Ly alpha blobs,' are extended (up to similar to 100 kpc), bright (L-Ly alpha greater than or similar to 10(43) erg s(-1)) clouds of Lya emitting gas that tend to lie in overdense regions at z similar to 2-5. The origin of the Lya emission remains unknown, but recent theoretical work suggests that measuring the polarization might discriminate among powering mechanisms. Here we present the first narrowband imaging polarimetry of a radio-loud Lya nebula, B3 J2330+3927, at z - 3.09, with an embedded active galactic nucleus (AGN). The AGN lies near the blob's Lya emission peak, and its radio lobes align roughly with the blob's major axis. With the SPOL polarimeter on the 6.5 m MMT telescope, we map the total (Ly alpha + continuum) polarization in a grid of circular apertures of a radius of 0.'' 6 (4.4 kpc), detecting a significant (>2 sigma) polarization fraction P-% in nine apertures and achieving strong upper limits (as low as 2%) elsewhere. P-% increases from <2% at similar to 5 kpc from the blob center to 17% at similar to 15-25 kpc. The detections are distributed asymmetrically, roughly along the nebula's major axis. The polarization angles theta are mostly perpendicular to this axis. Comparing the Ly alpha flux to that of the continuum and conservatively assuming that the continuum is highly polarized (20%-100%) and aligned with the total polarization, we place lower limits on the polarization of the Lya emission P-%,P-Ly alpha ranging from no significant polarization at similar to 5 kpc from the blob center to 3%-17% at 10-25 kpc. Like the total polarization, the Ly alpha polarization detections occur more often along the blob's major axis.</P>
Why Post-starburst Galaxies Are Now Quiescent
French, K. Decker,Zabludoff, Ann I.,Yoon, Ilsang,Shirley, Yancy,Yang, Yujin,Smercina, Adam,Smith, J. D.,Narayanan, Desika American Astronomical Society 2018 The Astrophysical journal Vol.861 No.2
<P>Post-starburst or 'E + A' galaxies are rapidly transitioning from star-forming to quiescence. While the current star formation rate (SFR) of post-starbursts is already at the level of early-type galaxies, we recently discovered that many have large CO-traced molecular gas reservoirs consistent with normal star-forming galaxies. These observations raise the question of why these galaxies have such low SFRs. Here we present an ALMA search for the denser gas traced by HCN (1-0) and HCO+ (1-0) in two CO-luminous, quiescent post-starburst galaxies. Intriguingly, we fail to detect either molecule. The upper limits are consistent with the low SFRs and with earlytype galaxies. The HCN/CO luminosity ratio upper limits are low compared to star-forming and even many earlytype galaxies. This implied low dense gas mass fraction explains the low SFRs relative to the CO-traced molecular gas and suggests that the state of the gas in post-starburst galaxies is unusual, with some mechanism inhibiting its collapse to denser states. We conclude that post-starbursts galaxies are now quiescent because little dense gas is available, in contrast to the significant CO-traced lower density gas reservoirs that still remain.</P>
Clocking the Evolution of Post-starburst Galaxies: Methods and First Results
French, K. Decker,Yang, Yujin,Zabludoff, Ann I.,Tremonti, Christy A. American Astronomical Society 2018 The Astrophysical journal Vol.862 No.1
<P>Detailed modeling of the recent star formation histories (SFHs) of post-starburst (or 'E+A') galaxies is impeded by the degeneracy between the time elapsed since the starburst ended (post-burst age), the fraction of stellar mass produced in the burst (burst strength), and the burst duration. To resolve this issue, we combine GALEX ultraviolet photometry, SDSS photometry and spectra, and new stellar population synthesis models to fit the SFHs of 532 post-starburst galaxies. In addition to an old stellar population and a recent starburst, 48% of the galaxies are best fit with a second recent burst. Lower stellar mass galaxies (log M-*/M-circle dot<10.5) are more likely to experience two recent bursts, and the fraction of their young stellar mass is more strongly anticorrelated with their total stellar mass. Applying our methodology to other, younger post-starburst samples, we identify likely progenitors to our sample and examine the evolutionary trends of molecular gas and dust content with post-burst age. We discover a significant (4 sigma) decline, with a 117-230 Myr characteristic depletion time, in the molecular gas to stellar mass fraction with the post-burst age. The implied rapid gas depletion rate of 2-150 M(circle dot)yr(-1) cannot be due to current star formation, given the upper limits on the current star formation rates in these post-starbursts. Nor are stellar winds or supernova feedback likely to explain this decline. Instead, the decline points to the expulsion or destruction of molecular gas in outflows, a possible smoking gun for active galactic nucleus feedback.</P>
Cai, Zheng,Fan, Xiaohui,Bian, Fuyan,Zabludoff, Ann,Yang, Yujin,Prochaska, J. Xavier,McGreer, Ian,Zheng, Zhen-Ya,Kashikawa, Nobunari,Wang, Ran,Frye, Brenda,Green, Richard,Jiang, Linhua American Astronomical Society 2017 The Astrophysical journal Vol.839 No.2
<P>Cosmological simulations suggest a strong correlation between high optical-depth Lya absorbers, which arise from the intergalactic medium, and 3D mass overdensities on scales of 10-30 h(-1) comoving Mpc. By examining the absorption spectra of similar to 80,000 QSO sight lines over a volume of 0.1 Gpc(3) in the Sloan Digital Sky Survey III (SDSS-III), we have identified an extreme overdensity, BOSS1441, which contains a rare group of strong Lya absorbers at z = 2.32 +/- 0.02. This absorber group is associated with six QSOs at the same redshift on a 30 comoving Mpc scale. Using Mayall/MOSAIC narrowband and broadband imaging, we detect Lya emitters (LAEs) down to 0.7 x L-Ly alpha ' * a and reveal a large-scale structure of LAEs in this field. Our follow-up LBT observations have spectroscopically confirmed 20 galaxies in the density peak. We show that BOSS1441 has an LAE overdensity of 10.8 +/- 2.6 on a 15 comoving Mpc scale, which could collapse to a massive cluster with M greater than or similar to 10(15) M-circle dot at z similar to 0. This overdensity is among the most massive large-scale structures at z similar to 2 discovered to date.</P>