Abstract
Observations of low-ionization state metal lines provide crucial insights into the interstellar medium (ISM) of galaxies, yet, disentangling the physical processes responsible for the ...emerging line profiles is difficult. This work investigates how mock spectra generated using a single galaxy in a radiation-hydrodynamical simulation can help us interpret observations of a real galaxy. We create 22,500 C
ii
and Si
ii
spectra from the virtual galaxy at different times and through multiple lines of sight and compare them with the 45 observations of low-redshift star-forming galaxies from the COS Legacy Spectroscopic SurveY (
classy
). We find that the mock profiles provide accurate replicates of the observations of 38 galaxies with a broad range of stellar masses (10
6
–10
9
M
⊙
) and metallicities (0.02–0.55
Z
⊙
). Additionally, we highlight that aperture losses explain the weakness of the fluorescent emission in several
classy
spectra and must be accounted for when comparing simulations to observations. Overall, we show that the evolution of a single simulated galaxy can produce a large diversity of spectra whose properties are representative of galaxies of comparable or smaller masses. Building upon these results, we explore the origin of the continuum, residual flux, and fluorescent emission in the simulation. We find that these different spectral features all emerge from distinct regions in the galaxy’s ISM, and their characteristics can vary as a function of the viewing angle. While these outcomes challenge simplified interpretations of down-the-barrel spectra, our results indicate that high-resolution simulations provide an optimal framework to interpret these observations.
Abstract To study the chemical evolution across cosmic epochs, we investigate Ne, S, Cl, and Ar abundance patterns in the Cosmic Origins Spectrograph Legacy Archive Spectroscopic SurveY (CLASSY). ...CLASSY comprises local star-forming galaxies (SFGs; 0.02 < z < 0.18) with enhanced star formation rates, making them strong analogues to high- z SFGs. With direct measurements of electron temperature, we derive accurate ionic abundances for all elements and assess ionization correction factors (ICFs) to account for unseen ions and derive total abundances. We find Ne/O, S/O, Cl/O, and Ar/O exhibit constant trends with gas-phase metallicity for 12+log(O/H) < 8.5 but significant correlation for Ne/O and Ar/O with metallicity for 12+log(O/H) > 8.5, likely due to ICFs. Thus, the applicability of the ICFs to integrated spectra of galaxies could bias results, underestimating true abundance ratios. Using CLASSY as a local reference, we assess the evolution of Ne/O, S/O, and Ar/O in galaxies at z > 3, finding no cosmic evolution of Ne/O, while the lack of direct abundance determinations for S/O and Ar/O can bias the interpretation of the evolution of these elements. We determine the fundamental metallicity relationship (FMR) for CLASSY and compare to the high-redshift FMR, finding no evolution. Finally, we perform the first mass–neon relationship analysis across cosmic epochs, finding a slight evolution to high Ne at later epochs. The robust abundance patterns of CLASSY galaxies and their broad range of physical properties provide essential benchmarks for interpreting the chemical enrichment of the early galaxies observed with the JWST.
The advent of the JWST has revolutionised our understanding of high-redshift
galaxies. In particular, the NIRCam instrument on-board JWST has revealed a
population of Hubble Space Telescope ...(HST)-dark galaxies that had previously
evaded optical detection, potentially due to significant dust obscuration,
quiescence, or simply extreme redshift. Here, we present the first NIRSpec
spectra of 23 HST-dark galaxies ($\mathrm{H-F444W>1.75}$), unveiling their
nature and physical properties. This sample includes both dusty and quiescent
galaxies with spectroscopic data from NIRSpec/PRISM, providing accurate
spectroscopic redshifts with $\mathrm{\overline{z}_{spec} = 4.1 \pm 0.7}$. The
spectral features demonstrate that, while the majority of HST-dark galaxies are
dusty, a substantial fraction, $\mathrm{13^{+9}_{-6} \%}$, are quiescent. For
the dusty galaxies, we have quantified the dust attenuation using the Balmer
decrement ($\mathrm{H\alpha / H\beta}$), finding attenuations $\mathrm{A_{V} >
2\ mag}$. We find that HST-dark dusty galaxies are $\mathrm{H\alpha}$ emitters
with equivalent widths spanning the range $\mathrm{ 68 A < EW_{H\alpha} < 550 A
}$, indicative of a wide range of recent star-formation activity. Whether dusty
or quiescent, we find that HST-dark galaxies are predominantly massive, with
85\% of the galaxies in the sample having masses $\mathrm{log(M_{*}/M_{\odot})
> 9.8}$. This pilot NIRSpec program reveals the diverse nature of HST-dark
galaxies and highlights the effectiveness of NIRSpec/PRISM spectroscopic
follow-up in distinguishing between dusty and quiescent galaxies and properly
quantifying their physical properties. Upcoming research utilising
higher-resolution NIRSpec data and combining JWST with ALMA observations will
enhance our understanding of these enigmatic and challenging sources.
The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen to cover similar properties to ...those seen at high z (z > 6). The prime high-level science product of CLASSY is accurately coadded UV spectra, ranging from ∼1000 to 2000 Å, derived from a combination of archival and new data obtained with HST's Cosmic Origins Spectrograph (COS). This paper details the multistage technical processes of creating this prime data product and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via C iii nebular emission. Despite changes in spectral resolution of up to ∼25% between individual data sets (due to changes in the COS line-spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in part to our signal-to-noise regime of S/N < 20.
Abstract
Far-ultraviolet (FUV; ∼1200–2000 Å) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, ...feedback processes, and reionization. The launch of the James Webb Space Telescope will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before; however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the Cosmic Origins Spectrograph Legacy Spectroscopic Survey (CLASSY) treasury and its first high-level science product, the CLASSY atlas. CLASSY builds on the Hubble Space Telescope (HST) archive to construct the first high-quality (S/N
1500 Å
≳ 5/resel), high-resolution (
R
∼ 15,000) FUV spectral database of 45 nearby (0.002 <
z
< 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar mass (6.2 < log
M
⋆
(
M
⊙
) < 10.1), star formation rate (−2.0 < log SFR (
M
⊙
yr
−1
) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O
32
< 38.0), reddening (0.02 <
E
(
B
−
V
) < 0.67), and nebular density (10 <
n
e
(cm
−3
) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with the
z
∼ 0 mass–metallicity relationship, but is offset to higher star formation rates by roughly 2 dex, similar to
z
≳ 2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.
The advent of the JWST has revolutionised our understanding of high-redshift galaxies. In particular, the NIRCam instrument on-board JWST has revealed a population of Hubble Space Telescope ...(HST)-dark galaxies that had previously evaded optical detection, potentially due to significant dust obscuration, quiescence, or simply extreme redshift. Here, we present the first NIRSpec spectra of 23 HST-dark galaxies (\(\mathrm{H-F444W>1.75}\)), unveiling their nature and physical properties. This sample includes both dusty and quiescent galaxies with spectroscopic data from NIRSpec/PRISM, providing accurate spectroscopic redshifts with \(\mathrm{\overline{z}_{spec} = 4.1 \pm 0.7}\). The spectral features demonstrate that, while the majority of HST-dark galaxies are dusty, a substantial fraction, \(\mathrm{13^{+9}_{-6} \%}\), are quiescent. For the dusty galaxies, we have quantified the dust attenuation using the Balmer decrement (\(\mathrm{H\alpha / H\beta}\)), finding attenuations \(\mathrm{A_{V} > 2\ mag}\). We find that HST-dark dusty galaxies are \(\mathrm{H\alpha}\) emitters with equivalent widths spanning the range \(\mathrm{ 68 A < EW_{H\alpha} < 550 A }\), indicative of a wide range of recent star-formation activity. Whether dusty or quiescent, we find that HST-dark galaxies are predominantly massive, with 85\% of the galaxies in the sample having masses \(\mathrm{log(M_{*}/M_{\odot}) > 9.8}\). This pilot NIRSpec program reveals the diverse nature of HST-dark galaxies and highlights the effectiveness of NIRSpec/PRISM spectroscopic follow-up in distinguishing between dusty and quiescent galaxies and properly quantifying their physical properties. Upcoming research utilising higher-resolution NIRSpec data and combining JWST with ALMA observations will enhance our understanding of these enigmatic and challenging sources.
Performing genetic studies in multiple human populations can identify disease risk alleles that are common in one population but rare in others, with the potential to illuminate pathophysiology, ...health disparities, and the population genetic origins of disease alleles. Here we analysed 9.2 million single nucleotide polymorphisms (SNPs) in each of 8,214 Mexicans and other Latin Americans: 3,848 with type 2 diabetes and 4,366 non-diabetic controls. In addition to replicating previous findings, we identified a novel locus associated with type 2 diabetes at genome-wide significance spanning the solute carriers SLC16A11 and SLC16A13 (P = 3.9 × 10(-13); odds ratio (OR) = 1.29). The association was stronger in younger, leaner people with type 2 diabetes, and replicated in independent samples (P = 1.1 × 10(-4); OR = 1.20). The risk haplotype carries four amino acid substitutions, all in SLC16A11; it is present at ~50% frequency in Native American samples and ~10% in east Asian, but is rare in European and African samples. Analysis of an archaic genome sequence indicated that the risk haplotype introgressed into modern humans via admixture with Neanderthals. The SLC16A11 messenger RNA is expressed in liver, and V5-tagged SLC16A11 protein localizes to the endoplasmic reticulum. Expression of SLC16A11 in heterologous cells alters lipid metabolism, most notably causing an increase in intracellular triacylglycerol levels. Despite type 2 diabetes having been well studied by genome-wide association studies in other populations, analysis in Mexican and Latin American individuals identified SLC16A11 as a novel candidate gene for type 2 diabetes with a possible role in triacylglycerol metabolism.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We investigate the stellar and nebular properties of 9 H II regions in the
spiral galaxy M101 with far-ultraviolet (FUV; ~900-2000 \r{A}) and optical
(~3200-10000 \r{A}) spectra. We detect ...significant C III 1907,1909 nebular
emission in 7 regions, but O III 1666 only in the lowest-metallicity region.
We produce new analytic functions of the carbon ICF as a function of
metallicity in order to perform a preliminary C/O abundance analysis. The FUV
spectra also contain numerous stellar emission and P-Cygni features that we fit
with luminosity-weighted combinations of single-burst Starburst99 and BPASS
models. We find that the best-fit Starburst99 models closely match the observed
very-high-ionization P-Cygni features, requiring very-hot, young (~< 3 Myr),
metal-enriched massive stars. The youngest stellar populations are strongly
correlated with broad He II emission, nitrogen Wolf-Rayet (WR) FUV and optical
spectral features, and enhanced N/O gas abundances. Thus, the short-lived WR
phase may be driving excess emission in several N P-Cygni wind features (955
\r{A}, 991 \r{A}, 1720 \r{A}) that bias the stellar continuum fits to higher
metallicities relative to the gas-phase metallicities. Accurate
characterization of these H II regions requires additional inclusion of WR
stars in the stellar population synthesis models. Our FUV spectra demonstrate
that the ~900-1200 \r{A} FUV can provide a strong test-bed for future WR
atmosphere and evolution models.
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