162 research outputs found
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The MOSDEF Survey: The Metallicity Dependence of X-Ray Binary Populations at z ∼ 2
Population synthesis models predict that high-mass X-ray binary (HMXB) populations produced in low-metallicity environments should be more X-ray luminous, a trend supported by studies of nearby galaxies. This trend may be responsible for the observed increase of the X-ray luminosity (L X) per star formation rate (SFR) with redshift due to the decrease of metallicity (Z) at fixed stellar mass as a function of redshift. To test this hypothesis, we use a sample of 79 z ∼ 2 star-forming galaxies with oxygen abundance measurements from the MOSDEF survey, which obtained rest-frame optical spectra for ∼1500 galaxies in the CANDELS fields at 1.37 < z < 3.80. Using Chandra data from the Chandra AEGIS-X Deep, Chandra Deep Field North, and Chandra Deep Field South surveys, we stack the X-ray data at the galaxy locations in bins of redshift and Z because the galaxies are too faint to be individually detected. In agreement with previous studies, the average L X/SFR of our z ∼ 2 galaxy sample is enhanced by ≈0.4-0.8 dex relative to local HMXB L X-SFR scaling relations. Splitting our sample by Z, we find that L X/SFR and Z are anticorrelated with 97% confidence. This observed Z dependence for HMXB-dominated galaxies is consistent with both the local L X-SFR-Z relation and a subset of population synthesis models. Although the statistical significance of the observed trends is weak owing to the low X-ray statistics, these results constitute the first direct evidence connecting the redshift evolution of L X/SFR and the Z dependence of HMXBs
Nuclear high-ionisation outflow in the Compton-thick AGN NGC6552 as seen by the JWST mid-infrared instrument
During the commissioning of the James Webb Space Telescope (JWST), the
mid-infrared instrument (MIRI) observed NGC6552 with the MIRI Imager and the
medium-resolution spectrograph (MRS). NGC6552 is an active galactic nucleus
(AGN) at redshift 0.0266 classified as a Seyfert 2 nucleus in the optical, and
Compton-thick AGN in X-rays. This work exemplifies and demonstrates the MRS
capabilities to study the mid-infrared (mid-IR) spectra and characterize the
physical conditions and kinematics of the ionized and molecular gas in the
nuclear regions of nearby galaxies. We obtained the nuclear, circumnuclear, and
central mid-IR spectra of NGC6552. They provide the first clear observational
evidence for a nuclear outflow in NGC6552. The outflow contributes to 677%
of the total line flux independent of the ionization potential (27 to 187 eV)
and critical densities (10 to 410 cm), showing an
average blue-shifted peak velocity of -12745 kms and an outflow
maximal velocity of 69880 kms. Since the mid-IR photons penetrate
dusty regions as efficiently as X-ray keV photons, we interpret these results
as the evidence for a highly ionized, non-stratified, AGN-powered, and fast
outflowing gas in a low density environment (few 10 cm) located
very close (<0.2kpc) to the Compton-thick AGN. Nine pure rotational molecular
Hydrogen lines are detected and spectrally resolved, and exhibit symmetric
Gaussian profiles, consistent with the galactic rotation, and with no evidence
of outflowing H material. We detect a warm H mass of
in the central region (1.8 kpc in diameter) of
the galaxy, with almost 30% of that mass in the circum-nuclear region. Line
ratios confirm that NGC6552 has a Seyfert nucleus with a black hole mass
estimated in the range of 0.6 to 6 million solar masses.Comment: 13 pages, 5 figures, 5 tables, accepted in A&
How dark the sky: the JWST backgrounds
We describe the sources of stray light and thermal background that affect
JWST observations; report actual backgrounds as measured from commissioning and
early science observations; compare those background levels to pre-launch
predictions; estimate the impact of the backgrounds on science performance; and
explore how the backgrounds probe the achieved configuration of the deployed
observatory. We find the observatory is limited by the irreducible
astrophysical backgrounds, rather than scattered stray light and thermal
self-emission, for all wavelengths micron, thus meeting the
level 1 requirement. This result was not assured given the open architecture
and thermal challenges of JWST, and is the result of meticulous attention to
stray light and thermal issues in the design, construction, integration, and
test phases. From background considerations alone, JWST will require less
integration time in the near-infrared compared to a system that just met the
stray light requirements; as such, JWST will be even more powerful than
expected for deep imaging at 1--5 micron. In the mid-infrared, the measured
thermal backgrounds closely match pre-launch predictions. The background near
10 micron is slightly higher than predicted before launch, but the impact on
observations is mitigated by the excellent throughput of MIRI, such that
instrument sensitivity will be as good as expected pre-launch. These measured
background levels are fully compatible with JWST's science goals and the Cycle
1 science program currently underway.Comment: Submitted to the "JWST Overview" special issue of PAS
The MOSDEF Survey: The Variation of the Dust Attenuation Curve with Metallicity
We derive a UV-optical stellar dust attenuation curve of galaxies at z = 1.4-2.6 as a function of gas-phase metallicity. We use a sample of 218 star-forming galaxies, excluding those with very young or heavily obscured star formation, from the MOSFIRE Deep Evolution Field survey with Hα, Hβ, and [N ii]λ 6585 spectroscopic measurements. We constrain the shape of the attenuation curve by comparing the average flux densities of galaxies sorted into bins of dust obscuration using Balmer decrements, i.e., Hα-to-Hβ luminosities. The average attenuation curve for the high-metallicity sample (, corresponding to ) has a shallow slope, identical to that of the Calzetti local starburst curve, and a significant UV 2175 - extinction bump that is ~0.5x the strength of the Milky Way bump. On the other hand, the average attenuation curve of the low-metallicity sample () has a steeper slope similar to that of the SMC curve, only consistent with the Calzetti slope at the 3σ level. The UV bump is not detected in the low-metallicity curve, indicating the relative lack of the small dust grains causing the bump at low metallicities. Furthermore, we find that on average the nebular reddening (E(B − V)) is a factor of 2 times larger than that of the stellar continuum for galaxies with low metallicities, while the nebular and stellar reddening are similar for galaxies with higher metallicities. The latter is likely due to a high surface density of dusty clouds embedding the star-forming regions but also reddening the continuum in the high-metallicity galaxies.Support for this work was provided by NASA through the
NASA Hubble Fellowship grant # HST-HF2-51420, awarded
by the Space Telescope Science Institute, which is operated by
the Association of Universities for Research in Astronomy,
Inc., for NASA, under contract NAS5-26555. Funding for the
MOSDEF survey was provided by NSF AAG grants AST1312780, 1312547, 1312764, and 1313171 and archival grant
AR-13907, provided by NASA through a grant from the Space
Telescope Science Institute. The data presented herein were
obtained at the W. M. Keck Observatory, which is operated as
a scientific partnership among the California Institute of
Technology, the University of California, and the National
Aeronautics and Space Administration. The Observatory was
made possible by the generous financial support of the W. M.
Keck Foundation. We are grateful to the MOSFIRE instrument
team for building this powerful instrument, and to Marc Kassis
at the Keck Observatory for his many valuable contributions to
the execution of the MOSDEF surve
Taking Census of Massive, Star-Forming Galaxies formed <1 Gyr After the Big Bang
Two decades of effort have been poured into both single-dish and interferometric millimeter-wave surveys of the sky to infer the volume density of dusty star-forming galaxies (DSFGs, with SFR>100M⊙ yr^(−1)) over cosmic time. Though obscured galaxies dominate cosmic star-formation near its peak at z∼2, the contribution of such heavily obscured galaxies to cosmic star-formation is unknown beyond z∼2.5 in contrast to the well-studied population of Lyman-break galaxies (LBGs) studied through deep, space- and ground-based pencil beam surveys in the near-infrared. Unlocking the volume density of DSFGs beyond z>3, particularly within the first 1 Gyr after the Big Bang is critical to resolving key open questions about early Universe galaxy formation: (1) What is the integrated star-formation rate density of the Universe in the first few Gyr and how is it distributed among low-mass galaxies (e.g. Lyman-break galaxies) and high-mass galaxies (e.g. DSFGs and quasar host galaxies)? (2) How and where do the first massive galaxies assemble? (3) What can the most extreme DSFGs teach us about the mechanisms of dust production (e.g. supernovae, AGB stars, grain growth in the ISM) <1 Gyr after the Big Bang? We summarize the types of observations needed in the next decade to address these questions
The MOSDEF-LRIS survey: connection between galactic-scale outflows and the properties of z ~ 2 star-forming galaxies
Large scale structure and cosmolog
The JWST FRESCO Survey: Legacy NIRCam/Grism Spectroscopy and Imaging in the two GOODS Fields
We present the JWST Cycle 1 53.8hr medium program FRESCO, short for “First Reionization Epoch Spectroscopically Complete Observations”. FRESCO covers 62 arcmin2 in each of the two GOODS/CANDELS fields for a total area of 124 arcmin2 exploiting JWST’s powerful new grism spectroscopic capabilities at near-infrared wavelengths. By obtaining ∼2hr deep NIRCam/grism observations with the F444W filter, FRESCO yields unprecedented spectra at R ∼ 1600 covering 3.8 to 5.0 μm for most galaxies in the NIRCam field-of-view. This setup enables emission line measurements over most of cosmic history, from strong PAH lines at z ∼ 0.2 − 0.5, to Paα and Paβ at z ∼ 1 − 3, HeI and [SIII] at z ∼ 2.5 − 4.5, Hα and [NII] at z ∼ 5 − 6.5, up to [OIII] and Hβ for z∼7-9 galaxies. FRESCO’s grism observations provide total line fluxes for accurately estimating galaxy stellar masses and calibrating slit-loss corrections of NIRSpec/MSA spectra in the same field. Additionally, FRESCO results in a mosaic of F182M, F210M, and F444W imaging in the same fields to a depth of ∼28.2 mag (5 σ in 032 diameter apertures). Here, we describe the overall survey design and the key science goals that can be addressed with FRESCO. We also highlight several, early science results, including: spectroscopic redshifts of Lyman break galaxies that were identified almost 20 years ago, the discovery of broad-line active galactic nuclei at z &gt; 4, and resolved Paα maps of galaxies at z ∼ 1.4. These results demonstrate the enormous power for serendipitous discovery of NIRCam/grism observations
Morpheus Reveals Distant Disk Galaxy Morphologies with JWST: The First AI/ML Analysis of JWST Images
The dramatic first images with JWST demonstrated its power to provide unprecedented spatial detail for galaxies in the high-redshift universe. Here, we leverage the resolution and depth of the JWST Cosmic Evolution Early Release Science Survey data in the Extended Groth Strip to perform pixel-level morphological classifications of galaxies in JWST F150W imaging using the Morpheus deep-learning framework for astronomical image analysis. By cross-referencing with existing photometric redshift catalogs from the Hubble Space Telescope (HST) CANDELS survey, we show that JWST images indicate the emergence of disk morphologies before z ∼ 2 and with candidates appearing as early as z ∼ 5. By modeling the light profile of each object and accounting for the JWST point-spread function, we find the high-redshift disk candidates have exponential surface brightness profiles with an average Sérsic index 〈n〉 = 1.04 and >90% displaying “disky” profiles (n < 2). Comparing with prior Morpheus classifications in CANDELS we find that a plurality of JWST disk galaxy candidates were previously classified as compact based on the shallower HST imagery, indicating that the improved optical quality and depth of the JWST helps to reveal disk morphologies that were hiding in the noise. We discuss the implications of these early disk candidates on theories for cosmological disk galaxy formation
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