We use the Sloan Digital Sky Survey (York et al.) data base to explore the effect of the disc inclination angle on the derived star formation rate (SFR), hence on the slope and width of the ...main-sequence (MS) relation for star-forming galaxies. We find that SFRs for nearly edge-on discs are underestimated by factors ranging from ~0.2 dex for low-mass galaxies up to ~0.4 dex for high-mass galaxies. This results in a substantially flatter MS relation for high-inclination discs compared to that for less inclined ones, though the global effect over the whole sample of star-forming galaxies is relatively minor, given the small fraction of high-inclination discs. However, we also find that galaxies with high-inclination discs represent a non-negligible fraction of galaxies populating the so-called green valley, with derived SFRs intermediate between the MS and those of quenched, passively evolving galaxies.
Light breeze in the local Universe Concas, A.; Popesso, P.; Brusa, M. ...
Astronomy and astrophysics (Berlin),
10/2017, Letnik:
606
Journal Article
Recenzirano
Odprti dostop
We analyze a complete spectroscopic sample of galaxies (~600 000) drawn from Sloan Digital Sky Survey (SDSS, DR7) to look for evidence of galactic winds in the local Universe. We focus on the shape ...of the OIIIλ5007 emission line as a tracer of ionizing gas outflows. We stack our spectra in a fine grid of star formation rate (SFR) and stellar mass to analyze the dependence of winds on the position of galaxies in the SFR versus mass diagram. We do not find any significant evidence of broad and shifted OIIIλ5007 emission line which we interpret as no evidence of outflowing ionized gas in the global population. We have also classified these galaxies as star-forming or AGN-dominated according to their position in the standard BPT diagram. We show how the average OIIIλ5007 profile changes as a function of the nature of the dominant ionizing source. We find that in the star-forming dominated source the oxygen line is symmetric and governed by the gravitational potential well. The AGN or composite AGN\star-formation activity objects, in contrast, display a prominent and asymmetric profile that can be well described by a broad Gaussian component that is blue-shifted from a narrow symmetric core. In particular, we find that the blue wings of the average OIIIλ5007 profiles are increasingly prominent in the LINERs and Seyfert galaxies. We conclude that, through the identification of strong bulk motion as traced by the warm ionized gas, in the low-redshift Universe, “pure” star-formation activity does not seem capable of driving ionized-gas outflows, while, the presence of optically selected AGN seems to play a primary role. We discuss the implications of these results for the role of the quenching mechanism in the present-day Universe.
Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local ...environment at z < 1.1. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS data sets. We distinguish group environments (...) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the main sequence (MS) of star-forming galaxies is not a linear relation and there is a flattening towards higher stellar masses (...), across all environments. At high redshift (0.5 < z < 1.1), the MS varies little with environment. At low redshift (0.15 < z < 0.5), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS towards low SFR is due to an increased fraction of bulge-dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disc-dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold (...) stellar mass, morphology and environment act together in driving the evolution of the star formation activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond z ~ 1. The environmental effects appear, instead, at lower redshifts and have a long time-scale. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We present six galaxies at
that show evidence of Lyman continuum (LyC) emission based on the newly acquired UV imaging of the Hubble Deep UV legacy survey (HDUV) conducted with the WFC3/UVIS ...camera on the
Hubble Space Telescope
(
HST
). At the redshift of these sources, the HDUV F275W images partially probe the ionizing continuum. By exploiting the
HST
multiwavelength data available in the HDUV/GOODS fields, models of the UV spectral energy distributions, and detailed Monte Carlo simulations of the intergalactic medium absorption, we estimate the absolute ionizing photon escape fractions of these galaxies to be very high—typically
(
for all sources at 90% likelihood). Our findings are in broad agreement with previous studies that found only a small fraction of galaxies with high escape fraction. These six galaxies compose the largest sample yet of LyC leaking candidates at
whose inferred LyC flux has been observed at
HST
resolution. While three of our six candidates show evidence of hosting an active galactic nucleus, two of these are heavily obscured and their LyC emission appears to originate from star-forming regions rather than the central nucleus. Extensive multiwavelength data in the GOODS fields, especially the near-IR grism spectra from the 3D-
HST
survey, enable us to study the candidates in detail and tentatively test some recently proposed indirect methods to probe LyC leakage. High-resolution spectroscopic follow-up of our candidates will help constrain such indirect methods, which are our only hope of studying
f
esc
at
in the
JWST
era.
HDUV: The Hubble Deep UV Legacy Survey Oesch, P. A.; Montes, M.; Reddy, N. ...
The Astrophysical journal. Supplement series,
07/2018, Letnik:
237, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We present the Hubble Deep UV Legacy Survey (HDUV), a 132-orbit imaging program with the WFC3/UVIS camera on board the
Hubble Space Telescope
(
HST
). The HDUV extends and builds on the few ...previous UV imaging surveys in the two GOODS/CANDELS-Deep fields to provide deep images over a total area of ∼100 arcmin
2
in the two filters F275W and F336W. Our release also includes all the F275W imaging data taken by the CANDELS survey, which were aligned using a novel approach and combined with the HDUV survey data. By reaching depths of 27.5–28.0 mag (5
σ
in 0.″4 apertures), these are the deepest high-resolution UV data over such a large area taken to date. Such unique UV imaging enables a wide range of science by the community. A few of the main goals of the HDUV survey are as follows: (1) to provide a complete sample of faint star-forming galaxies at
z
∼ 1–3; (2) to constrain the ionizing photon escape fraction from galaxies at
z
∼ 2–3; and (3) to track the build-up of bulges and the disappearance of clumpy disk galaxies through reliable internal stellar population properties at sub-kiloparsec resolution out to
z
∼ 3. The addition of the HDUV data further enhances the legacy value of the two GOODS/CANDELS-Deep fields, which now include deep 11-band
HST
imaging, as well as very deep ancillary data from X-ray to radio, enabling unique multi-wavelength studies. Here, we provide an overview of the survey design, describe the data reduction, and highlight a few basic analyses of the images that are available to the community as high-level science products, via the Mikulski Archive for Space Telescopes.
ABSTRACT
We use dust masses (Mdust) derived from far-infrared data and molecular gas masses (Mmol) based on CO luminosity to calibrate proxies based on a combination of the galaxy Balmer decrement, ...disc inclination, and gas metallicity. We use such proxies to estimate Mdust and Mmol in the local SDSS sample of star-forming galaxies (SFGs). We study the distribution of Mdust and Mmol along and across the main sequence (MS) of SFGs. We find that Mdust and Mmol increase rapidly along the MS with increasing stellar mass (M*), and more marginally across the MS with increasing SFR (or distance from the relation). The dependence on M* is sub-linear for both Mdust and Mmol. Thus, the fraction of dust (fdust) and molecular gas mass (fmol) decreases monotonically towards large M*. The star formation efficiency (SFE, inverse of the molecular gas depletion time) depends strongly on the distance from the MS and it is constant along the MS. As nearly all galaxies in the sample are central galaxies, we estimate the dependence of fdust and fgas on the host halo mass and find a tight anticorrelation. As the region where the MS is bending is numerically dominated by massive haloes, we conclude that the bending of the MS is due to a lower availability of molecular gas mass in massive haloes rather than a lower efficiency in forming stars.
Abstract
Study Objectives:
Severe sleep restriction results in elevated evening cortisol levels. We examined whether this relative hypercortisolism is associated with alterations in the ...pituitary–adrenocortical response to evening corticotropin-releasing hormone (CRH) stimulation.
Methods:
Eleven subjects participated in 2 sessions (2 nights of 10 hours vs. 4 hours in bed) in randomized order. Sleep was polygraphically recorded. After the second night of each session, blood was sampled at 20-minute intervals from 09:00 to 24:00 for adrenocorticotropic hormone (ACTH) and cortisol measurements, and perceived stress was assessed hourly. Ovine CRH was injected at 18:00 (1 µg/kg body weight).
Results:
Prior to CRH injection, baseline ACTH, but not cortisol, levels were elevated after sleep restriction. Relative to the well-rested condition, sleep restriction resulted in a 27% decrease in overall ACTH response to CRH (estimated by the incremental area under the curve from 18:00 to 24:00; p = .002) while the cortisol response was decreased by 21% (p = .083). Further, the magnitude of these decreases was correlated with the individual amount of sleep loss (ACTH: r
Sp = −0.65, p = .032; cortisol: r
Sp = −0.71, p = .015). The acute post-CRH increment of cortisol was reduced (p = .002) without changes in ACTH reactivity, suggesting decreased adrenal sensitivity. The rate of decline from peak post-injection levels was reduced for cortisol (p = .032), but not for ACTH. Scores of perceived stress were unaffected by CRH injection and were low and similar under both sleep conditions.
Conclusions:
Sleep restriction is associated with a reduction of the overall ACTH and cortisol responses to evening CRH stimulation, and a reduced reactivity and slower recovery of the cortisol response.
PDF
