Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Xinfeng Xu
Alaina Henry
Timothy Heckman
John Chisholm
Rui Marques-Chaves
Floriane Leclercq
Danielle A. Berg
Anne Jaskot
Daniel Schaerer
Gábor Worseck
Ricardo O. Amorín
Hakim Atek
Matthew Hayes
Zhiyuan Ji
Göran Östlin
Alberto Saldana-Lopez
Trinh Thuan
Abstract： The Mg II 2796, 2803 doublet has been suggested to be a useful indirect indicator for the escape of Ly-alpha and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg II or strong LyC emission. Here we present the first study of Mg II probing a large dynamic range of galaxy properties, using newly obtained high signal-to-noise, moderate-resolution spectra of Mg II for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg II profiles ranging from strong emission to P-Cygni profiles, and to pure absorption. We find there is a significant trend (with a possibility of spurious correlations of ~ 2%) that galaxies detected as strong LyC Emitters (LCEs) also show larger equivalent widths of Mg II emission, and non-LCEs tend to show evidence of more scattering and absorption features in Mg II We then find Mg II strongly correlates with Ly-alpha in both equivalent width and escape fraction, regardless of whether the emission or absorption dominates the Mg II profiles. Furthermore, we present that, for galaxies categorized as Mg II emitters (MgE), one can adopt the information of Mg II, metallicity, and dust to estimate the escape fraction of LyC within a factor of 3. These findings confirm that Mg II lines can be used as a tool to select galaxies as LCEs and to serve as an indirect indicator for the escape of Ly-alpha and LyC.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Xinfeng Xu
Timothy Heckman
Alaina Henry
Danielle A. Berg
John Chisholm
Bethan L. James
Crystal L. Martin
Daniel P. Stark
Matthew Hayes
Karla Z. Arellano-Cordova
Cody Carr
Mason Huberty
Matilde Mingozzi
Claudia Scarlata
Yuma Sugahara
Abstract： Galaxy formation and evolution are regulated by the feedback from galactic winds. Absorption lines provide the most widely available probe of winds. However, since most data only provide information integrated along the line-of-sight, they do not directly constrain the radial structure of the outflows. In this paper, we present a method to directly measure the gas electron density in outflows (ne), which in turn yields estimates of outflow cloud properties (e.g., density, volume filling-factor, and sizes/masses). We also estimate the distance (r) from the starburst at which the observed densities are found. We focus on 22 local star-forming galaxies primarily from the COS Legacy Archive Spectroscopic SurveY (CLASSY). In half of them, we detect absorption lines from fine structure excited transitions of Si II (i.e., Si II*). We determine ne from relative column densities of Si II and Si II*, given Si II* originates from collisional excitation by free electrons. We find that the derived ne correlates well with the galaxy's star-formation rate per unit area. From photoionization models or assuming the outflow is in pressure equilibrium with the wind fluid, we get r ~ 1 to 2 * rstar or ~ 5 * rstar, respectively, where rstar is the starburst radius. Based on comparisons to theoretical models of multi-phase outflows, nearly all of the outflows have cloud sizes large enough for the clouds to survive their interaction with the hot wind fluid. Most of these measurements are the first-ever for galactic winds detected in absorption lines and, thus, will provide important constraints for future models of galactic winds.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Xinfeng Xu
Timothy Heckman
Alaina Henry
Danielle A. Berg
John Chisholm
Bethan L. James
Crystal L. Martin
Daniel P. Stark
Alessandra Aloisi
Ricardo O. Amorín
Karla Z. Arellano-Córdova
Rongmon Bordoloi
Stéphane Charlot
Zuyi Chen
Matthew Hayes
Matilde Mingozzi
Yuma Sugahara
Lisa J. Kewley
Masami Ouchi
Claudia Scarlata
Abstract： We report the results of analyses of galactic outflows in a sample of 45 low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY (CLASSY), augmented by five additional similar starbursts with COS data. The outflows are traced by blueshifted absorption-lines of metals spanning a wide range of ionization potential. The high quality and broad spectral coverage of CLASSY data enable us to disentangle the absorption due to the static ISM from that due to outflows. We further use different line multiplets and doublets to determine the covering fraction, column density, and ionization state as a function of velocity for each outflow. We measure the outflow's mean velocity and velocity width, and find that both correlate in a highly significant way with the star-formation rate, galaxy mass, and circular velocity over ranges of four orders-of-magnitude for the first two properties. We also estimate outflow rates of metals, mass, momentum, and kinetic energy. We find that, at most, only about 20% of silicon created and ejected by supernovae in the starburst is carried in the warm phase we observe. The outflows' mass-loading factor increases steeply and inversely with both circular and outflow velocity (log-log slope $\sim$ -1.6), and reaches $\sim 10$ for dwarf galaxies. We find that the outflows typically carry about 10 to 100% of the momentum injected by massive stars and about 1 to 20% of the kinetic energy. We show that these results place interesting constraints on, and new insights into, models and simulations of galactic winds.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Matilde Mingozzi
Bethan L. James
Karla Z. Arellano-Córdova
Danielle A. Berg
Peter Senchyna
John Chisholm
Jarle Brinchmann
Alessandra Aloisi
Ricardo Amorín
Stephane Charlot
Anna Feltre
Matthew J. Hayes
Tim Heckman
Alaina Henry
Svea Hernandez
Nimisha Kumari
Claus Leitherer
Mario Llerena
Crystal L. Martin
Themiya Nanayakkara
Abstract： The COS Legacy Archive Spectroscopic SurveY (CLASSY) HST/COS treasury program provides the first high-resolution spectral catalogue of 45 local high-z analogues in the UV (1200-2000{\AA}) to investigate their stellar and gas properties. We present a toolkit of UV interstellar medium (ISM) diagnostics, analyzing the main emission lines of CLASSY spectra (i.e., NIV]{\lambda}{\lambda}1483,87, CIV{\lambda}{\lambda}1548,51, HeII{\lambda}1640, OIII]{\lambda}{\lambda}1661,6, SiIII]{\lambda}{\lambda}1883,92, CIII]{\lambda}{\lambda}1907,9). Specifically, we focus our investigation on providing accurate diagnostics for reddening, electron density and temperature, gas-phase metallicity and ionization parameter, taking into account the different ionization zones of the ISM. We calibrate our UV toolkit using well-known optical diagnostics, analyzing archival optical spectra for all the CLASSY targets. We find that UV density diagnostics estimate ne values that are ~1-2 dex higher (e.g., ne(CIII]{\lambda}{\lambda}1907,9)~10^4cm^{-3}) than those inferred from their optical counterparts (e.g., ne([SII]{\lambda}{\lambda}6717,31)~10^2cm^{-3}). Te derived from the hybrid ratio OIII]{\lambda}1666/[OIII]{\lambda}5007 proves to be a reliable Te diagnostic, with differences in 12+log(O/H) within ~+/-0.3dex. We also investigate the relation between the stellar and gas E(B-V), finding consistent values at high specific star formation rates, while at low sSFR we confirm an excess of dust attenuation in the gas. Finally, we investigate UV line ratios and equivalent widths to provide correlations with 12+log(O/H) and log(U), but note there are degeneracies between the two. With this suite of UV-based diagnostics, we illustrate the pivotal role CLASSY plays in understanding the chemical and physical properties of high-z systems that JWST can observe in the rest-frame UV.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Xinfeng Xu
Alaina Henry
Timothy Heckman
John Chisholm
Gábor Worseck
Max Gronke
Anne Jaskot
Stephan R. McCandliss
Sophia R. Flury
Mauro Giavalisco
Zhiyuan Ji
Ricardo O. Amorín
Danielle A. Berg
Sanchayeeta Borthakur
Nicolas Bouche
Cody Carr
Dawn K. Erb
Harry Ferguson
Thibault Garel
Matthew Hayes
Abstract： Star-forming galaxies are considered the likeliest source of the H I ionizing Lyman Continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above z >~ 6, the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of indirect indicators for LyC that can be calibrated at lower redshifts and applied in the Epoch of Reionization. Emission from Mg II \ly\ly 2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph observations for 8 LyC emitter candidates, selected to have strong Mg II emission lines. We securely detect LyC emission in 50% (4/8) galaxies with 2$\sigma$ significance. This high detection rate suggests that strong Mg II emitters might be more likely to leak LyC than similar galaxies without strong Mg II. Using photoionization models, we constrain the escape fraction of Mg II as ~ 15 -- 60%. We confirm that the escape fraction of Mg II correlates tightly with that of Lyman-alpha (LyA), which we interpret as an indication that the escape fraction of both species is controlled by resonant scattering in the same low column density gas. Furthermore, we show that the combination of the Mg II emission and dust attenuation can be used to estimate the escape fraction of LyC statistically. These findings confirm that Mg II emission can be adopted to estimate the escape fraction of LyA and LyC in local star-forming galaxies and may serve as a useful indirect indicator at the Epoch of Reionization.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Micaela B. Bagley
Nor Pirzkal
Steven L. Finkelstein
Casey Papovich
Danielle A. Berg
Jennifer M. Lotz
Gene C. K. Leung
Henry C. Ferguson
Anton M. Koekemoer
Mark Dickinson
Jeyhan S. Kartaltepe
Dale D. Kocevski
Rachel S. Somerville
L. Y. Aaron Yung
Bren E. Backhaus
Caitlin M. Casey
Marco Castellano
Óscar A. Chávez Ortiz
Katherine Chworowsky
Isabella G. Cox
Abstract： We present the Next Generation Deep Extragalactic Exploratory Public (NGDEEP)
Survey, a deep slitless spectroscopic and imaging Cycle 1 JWST treasury survey
designed to constrain feedback mechanisms in low-mass galaxies across cosmic
time. NGDEEP targets the Hubble Ultra Deep Field (HUDF) with NIRISS slitless
spectroscopy (f~1.2e-18 erg/s/cm^2, 5sigma) to measure metallicities and
star-formation rates (SFRs) for low-mass galaxies through the peak of the
cosmic SFR density (0.5
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
S. R. Kulkarni
Fiona A. Harrison
Brian W. Grefenstette
Hannah P. Earnshaw
Igor Andreoni
Danielle A. Berg
Joshua S. Bloom
S. Bradley Cenko
Ryan Chornock
Jessie L. Christiansen
Michael W. Coughlin
Alexander Wuollet Criswell
Behnam Darvish
Kaustav K. Das
Kishalay De
Luc Dessart
Don Dixon
Bas Dorsman
Kareem El-Badry
Christopher Evans
Abstract： UVEX is a proposed medium class Explorer mission designed to provide crucial missing capabilities that will address objectives central to a broad range of modern astrophysics. The UVEX design has two co-aligned wide-field imagers operating in the FUV and NUV and a powerful broadband medium resolution spectrometer. In its two-year baseline mission, UVEX will perform a multi-cadence synoptic all-sky survey 50/100 times deeper than GALEX in the NUV/FUV, cadenced surveys of the Large and Small Magellanic Clouds, rapid target of opportunity followup, as well as spectroscopic followup of samples of stars and galaxies. The science program is built around three pillars. First, UVEX will explore the low-mass, low-metallicity galaxy frontier through imaging and spectroscopic surveys that will probe key aspects of the evolution of galaxies by understanding how star formation and stellar evolution at low metallicities affect the growth and evolution of low-metallicity, low-mass galaxies in the local universe. Such galaxies contain half the mass in the local universe, and are analogs for the first galaxies, but observed at distances that make them accessible to detailed study. Second, UVEX will explore the dynamic universe through time-domain surveys and prompt spectroscopic followup capability will probe the environments, energetics, and emission processes in the early aftermaths of gravitational wave-discovered compact object mergers, discover hot, fast UV transients, and diagnose the early stages of stellar explosions. Finally, UVEX will become a key community resource by leaving a large all-sky legacy data set, enabling a wide range of scientific studies and filling a gap in the new generation of wide-field, sensitive optical and infrared surveys provided by the Rubin, Euclid, and Roman observatories. This paper discusses the scientific potential of UVEX, and the broad scientific program.
Peer Review Status:Awaiting Review
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