The Large Magellanic Cloud's ∼30\sim30 Kiloparsec Bow Shock and its Impact on the Circumgalactic Medium

The interaction between the supersonic motion of the Large Magellanic Cloud (LMC) and the Circumgalactic Medium (CGM) is expected to result in a bow shock that leads the LMC's gaseous disk. In this letter, we use hydrodynamic simulations of the LMC's recent infall to predict the extent of this shock and its effect on the Milky Way's (MW) CGM. The simulations clearly predict the existence of an asymmetric shock with a present day stand-off radius of $\sim6.7$ kpc and a transverse diameter of $\sim30$ kpc. Over the past 500 Myr, $\sim8\%$ of the MW's CGM in the southern hemisphere should have interacted with the shock front. This interaction may have had the effect of smoothing over inhomogeneities and increasing mixing in the MW CGM. We find observational evidence of the existence of the bow shock in recent $H\alpha$ maps of the LMC, providing a potential explanation for the envelope of ionized gas surrounding the LMC. Furthermore, the interaction of the bow shock with the MW CGM may also explain observations of ionized gas surrounding the Magellanic Stream. Using recent orbital histories of MW satellites, we find that many satellites have likely interacted with the LMC shock. Additionally, the dwarf galaxy Ret2 is currently sitting inside the shock, which may impact the interpretation of reported gamma ray excess in Ret2. This work highlights bow shocks associated with infalling satellites are an under-explored, yet potentially very important dynamical mixing process in the circumgalactic and intracluster media.Comment: Submitted to ApJ Letters, 5 figures and 1 table. Comments welcome

Star Formation Suppression by Tidal Removal of Cold Molecular Gas from an Intermediate-redshift Massive Post-starburst Galaxy

Observations and simulations have demonstrated that star formation in galaxies must be actively suppressed to prevent the formation of overly massive galaxies. Galactic outflows driven by stellar feedback or supermassive black hole accretion are often invoked to regulate the amount of cold molecular gas available for future star formation but may not be the only relevant quenching processes in all galaxies. We present the discovery of vast molecular tidal features extending up to 64 kpc outside of a massive z = 0.646 post-starburst galaxy that recently concluded its primary star-forming episode. The tidal tails contain (1.2 ± 0.1) × 1010 M⊙ of molecular gas, 47% ± 5% of the total cold gas reservoir of the system. Both the scale and magnitude of the molecular tidal features are unprecedented compared to all known nearby or high-redshift merging systems. We infer that the cold gas was stripped from the host galaxies during the merger, which is most likely responsible for triggering the initial burst phase and the subsequent suppression of star formation. While only a single example, this result shows that galaxy mergers can regulate the cold gas contents in distant galaxies by directly removing a large fraction of the molecular gas fuel, and plausibly suppress star formation directly, a qualitatively different physical mechanism than feedback-driven outflows

The Compact Structures of Massive z ∼ 0.7 Post-starburst Galaxies in the SQuIGGL⃗E Sample

We present structural measurements of 145 spectroscopically selected intermediate-redshift (z ∼ 0.7), massive (M⋆ ∼ 1011 M⊙) post-starburst galaxies from the $\mathrm{SQuIGG}\vec{L}{\rm{E}}$ sample measured using wide-depth Hyper Suprime-Cam i-band imaging. This deep imaging allows us to probe the sizes and structures of these galaxies, which we compare to a control sample of star-forming and quiescent galaxies drawn from the LEGA-C Survey. We find that post-starburst galaxies systematically lie ∼0.1 dex below the quiescent mass–size (half-light radius) relation, with a scatter of ∼0.2 dex. This finding is bolstered by nonparametric measures, such as the Gini coefficient and the concentration, which also reveal these galaxies to have more compact light profiles than both quiescent and star-forming populations at similar mass and redshift. The sizes of post-starburst galaxies show either negative or no correlation with the time since quenching, such that more recently quenched galaxies are larger or similarly sized. This empirical finding disfavors the formation of post-starburst galaxies via a purely central burst of star formation that simultaneously shrinks the galaxy and shuts off star formation. We show that the central densities of post-starburst and quiescent galaxies at this epoch are very similar, in contrast with their effective radii. The structural properties of z ∼ 0.7 post-starburst galaxies match those of quiescent galaxies that formed in the early universe, suggesting that rapid quenching in the present epoch is driven by a similar mechanism to the one at high redshift

Rest-frame near-infrared sizes of galaxies at cosmic noon: objects in JWST's mirror are smaller than they appeared

Galaxy sizes and their evolution over cosmic time have been studied for decades and serve as key tests of galaxy formation models. However, at $z\gtrsim1$ these studies have been limited by a lack of deep, high-resolution rest-frame infrared imaging that accurately traces galaxy stellar mass distributions. Here, we leverage the new capabilities of the James Webb Space Telescope to measure the 4.4$\mu$m sizes of ${\sim}1000$ galaxies with $\log{\rm{M}_*/\rm{M}_\odot}\ge9$ and $1.0\le z \le 2.5$ from public CEERS imaging in the EGS deep field. We compare the sizes of galaxies measured from NIRCam imaging at 4.4$\mu$m ($\lambda_{\mathrm{rest}}\sim1.6\mu$m) with sizes measured at $1.5\mu$m ($\lambda_{\mathrm{rest}}\sim5500$A). We find that, on average, galaxy half-light radii are $\sim8$% smaller at 4.4$\mu$m than 1.5$\mu$m in this sample. This size difference is markedly stronger at higher stellar masses and redder rest-frame $V-J$ colors: galaxies with ${\rm M}_* \sim 10^{11}\,{\rm M}_\odot$ have 4.4$\mu$m sizes that are $\sim 25$% smaller than their 1.5$\mu$m sizes. Our results indicate that galaxy mass profiles are significantly more compact than their rest-frame optical light profiles at cosmic noon, and demonstrate that spatial variations in age and attenuation are important, particularly for massive galaxies. The trend that we find here impacts our understanding of the size growth and evolution of galaxies, and suggests that previous studies based on rest-frame optical light may not have captured the mass-weighted structural evolution of galaxies. This paper represents a first step towards a new understanding of the morphologies of early massive galaxies enabled by JWST's infrared window into the distant universe.Comment: Accepted to ApJL. 10 pages, 4 figures, 1 table with full size catalog in F150W and F444

The FENIKS Survey: Spectroscopic Confirmation of Massive Quiescent Galaxies at z ~ 3-5

The measured ages of massive, quiescent galaxies at $z\sim 3-4$ imply that massive galaxies quench as early as $z\sim 6$. While the number of spectroscopic confirmations of quiescent galaxies at $z < 3$ has increased over the years, there are only a handful at $z > 3.5$. We report spectroscopic redshifts of one secure ($z=3.757$) and two tentative ($z = 3.336$, $z=4.673$) massive ($\log(M_\ast/M_\odot) > 10.3$) quiescent galaxies with 11 hours of Keck/MOSFIRE $K$-band observations. Our candidates were selected from the FENIKS survey, which uses deep Gemini/Flamingos-2 $K_b$ $K_r$ imaging optimized for increased sensitivity to the characteristic red colors of galaxies at $z > 3$ with strong Balmer/4000 \AA\ breaks. The rest-frame $UVJ$ and $(ugi)_s$ colors of 3/4 quiescent candidates are consistent with $1-2$ Gyr old stellar populations. This places these galaxies as the oldest objects at these redshifts, and challenges the notion that quiescent galaxies at $z > 3$ are all recently-quenched, "post-starburst'' galaxies. Our spectroscopy shows that the other quiescent-galaxy candidate is a broad-line AGN ($z = 3.594$) with strong, redshifted $H\beta$+[O III] emission with a velocity offset $>1000$ km/s, indicative of a powerful outflow. The star-formation history of our highest redshift candidate suggests that its progenitor was already in place by $z \sim 7-11$, reaching $\sim$ 10$^{11} M_{\odot}$ by $z \simeq 10$. These observations reveal the limit of what is possible with deep near-infrared photometry and targeted spectroscopy from the ground and demonstrate that secure spectroscopic confirmation of quiescent galaxies at $z > 4$ is only feasible with JWST.Comment: 20 pages, 11 figures, submitted to Ap

Two Remarkably Luminous Galaxy Candidates at z≈11−13z\approx11-13 Revealed by JWST

The first few hundred Myrs at $z>10$ mark the last major uncharted epoch in the history of the Universe, where only a single galaxy (GNz11 at $z\approx11$) is currently spectroscopically confirmed. Here we present a search for luminous $z>10$ galaxies with $JWST$/NIRCam photometry spanning $\approx1-5\mu$m and covering 49 arcmin$^{2}$ from the public $JWST$ Early Release Science programs (CEERS and GLASS). Our most secure candidates are two $M_{\rm{UV}}\approx-21$ systems: GLASS-z13 and GLASS-z11. These galaxies display abrupt $\gtrsim2.5$ mag breaks in their spectral energy distributions, consistent with complete absorption of flux bluewards of Lyman-$\alpha$ that is redshifted to $z\approx13$ and $z\approx11$. Lower redshift interlopers such as dusty quiescent galaxies with strong Balmer breaks would be comfortably detected at $>5\sigma$ in multiple bands where instead we find no flux. From SED modeling we infer that these galaxies have already built up $\sim 10^9$ solar masses in stars over the $\lesssim300-400$ Myrs after the Big Bang. The brightness of these sources enable morphological constraints. Tantalizingly, GLASS-z11 shows a clearly extended exponential light profile, potentially consistent with a disk galaxy of $r_{\rm{50}}\approx0.7$ kpc. These sources, if confirmed, join GNz11 in defying number density forecasts for luminous galaxies based on Schechter UV luminosity functions, which require a survey area $>10\times$ larger than we have studied here to find such luminous sources at such high redshifts. They extend evidence from lower redshifts for little or no evolution in the bright end of the UV luminosity function into the cosmic dawn epoch, with implications for just how early these galaxies began forming. This, in turn, suggests that future deep $JWST$ observations may identify relatively bright galaxies to much earlier epochs than might have been anticipated.Comment: Submitted to ApJL. Figs. 1 and 2 summarize the candidates, Fig. 3 places the brightness of these systems in context, Fig. 4 shows the morphology, Fig. 5 explores implications for the UVLF. Comments warmly welcome

JWST reveals a population of ultra-red, flattened disk galaxies at 2<z<6 previously missed by HST

With just a month of data, JWST is already transforming our view of the Universe, revealing and resolving starlight in unprecedented populations of galaxies. Although ``HST-dark" galaxies have previously been detected at long wavelengths, these observations generally suffer from a lack of spatial resolution which limits our ability to characterize their sizes and morphologies. Here we report on a first view of starlight from a subset of the HST-dark population that are bright with JWST/NIRCam (4.4$\mu$m<24.5mag) and very faint or even invisible with HST ($<$1.6$\mu$m). In this Letter we focus on a dramatic and unanticipated population of physically extended galaxies ($\gtrsim$0.17''). These 12 galaxies have photometric redshifts $2<z<6$, high stellar masses $M_{\star}\gtrsim 10^{10}~M_{\odot}$, and significant dust-attenuated star formation. Surprisingly, the galaxies have elongated projected axis ratios at 4.4$\mu$m, suggesting that the population is disk-dominated or prolate. Most of the galaxies appear red at all radii, suggesting significant dust attenuation throughout. We refer to these red, disky, HST-dark galaxies as Ultra-red Flattened Objects (UFOs). With $r_e$(F444W)$\sim1-2$~kpc, the galaxies are similar in size to compact massive galaxies at $z\sim2$ and the cores of massive galaxies and S0s at $z\sim0$. The stellar masses, sizes, and morphologies of the sample suggest that some could be progenitors of lenticular or fast-rotating galaxies in the local Universe. The existence of this population suggests that our previous censuses of the universe may have missed massive, dusty edge-on disks, in addition to dust-obscured starbursts

DESI Survey Validation Spectra Reveal an Increasing Fraction of Recently Quenched Galaxies at z∼1z\sim1

We utilize $\sim17000$ bright Luminous Red Galaxies (LRGs) from the novel Dark Energy Spectroscopic Instrument Survey Validation spectroscopic sample, leveraging its deep ($\sim2.5$ hour/galaxy exposure time) spectra to characterize the contribution of recently quenched galaxies to the massive galaxy population at $0.4<z<1.3$. We use Prospector to infer non-parametric star formation histories and identify a significant population of post-starburst galaxies that have joined the quiescent population within the past $\sim1$ Gyr. The highest redshift subset (277 at $z>1$) of our sample of recently quenched galaxies represents the largest spectroscopic sample of post-starburst galaxies at that epoch. At $0.4<z<0.8$, we measure the number density of quiescent LRGs, finding that recently quenched galaxies constitute a growing fraction of the massive galaxy population with increasing lookback time. Finally, we quantify the importance of this population amongst massive ($\mathrm{log}(M_\star/M_\odot)>11.2$) LRGs by measuring the fraction of stellar mass each galaxy formed in the Gyr before observation, $f_{\mathrm{1 Gyr}}$. Although galaxies with $f_{\mathrm{1 Gyr}}>0.1$ are rare at $z\sim0.4$ ($\lesssim 0.5\%$ of the population), by $z\sim0.8$ they constitute $\sim3\%$ of massive galaxies. Relaxing this threshold, we find that galaxies with $f_\mathrm{1 Gyr}>5\%$ constitute $\sim10\%$ of the massive galaxy population at $z\sim0.8$. We also identify a small but significant sample of galaxies at $z=1.1-1.3$ that formed with $f_{\mathrm{1 Gyr}}>50\%$, implying that they may be analogues to high-redshift quiescent galaxies that formed on similar timescales. Future analysis of this unprecedented sample promises to illuminate the physical mechanisms that drive the quenching of massive galaxies after cosmic noon.Comment: Submitted to ApJ Letters after DESI Collaboration Review. 14 pages, 5 figures, comments welcome