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Register a new userThe Strength of the 2175AA Feature in the Attenuation Curves of Galaxies at 0.1<z<3
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We update the spectral modeling code MAGPHYS to include a 2175AA absorption feature in its UV-to-near-IR dust attenuation prescription. This allows us to determine the strength of this feature and the shape of the dust attenuation curve in ~5000 star-forming galaxies at 0.1<z<3 in the COSMOS field. We find that a 2175AA absorption feature of ~1/3 the strength of that in the Milky Way is required for models to minimize residuals. We characterize the total effective dust attenuation curves as a function of several galaxy properties and find that the UV slopes of the attenuation curve for COSMOS galaxies show a strong dependence with star formation rate (SFR) and total dust attenuation ($A_V$), such that galaxies with higher SFR and $A_V$ have shallower curves and vice versa. These results are consistent with expectations from radiative transfer that attenuation curves become shallower as the effective dust optical depth increases. We do not find significant trends in the strength of the 2175AA absorption feature as a function of galaxy properties, but this may result from the high uncertainties associated with this measurement. The updated code is publicly available online.
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We determine the extinction curve in the z_l=0.83 lens galaxy of the gravitational lens SBS0909+532 from the wavelength dependence of the flux ratio between the lensed quasar images (z_s=1.38) from 3400 to 9200AA. It is the first measurement of an extinction curve at a cosmological distance of comparable quality to those obtained within the Galaxy. The extinction curve has a strong 2175AA feature, a noteworthy fact because it has been weak or non-existent in most estimates of extinction curves outside the Galaxy. The extinction curve is fitted well by a standard $R_V=2.1pm0.9$ Galactic extinction curve. If we assume standard Galactic extinction laws, the estimated dust redshift of $z=0.88pm0.02$ is in good agreement with the spectroscopic redshift of the lens galaxy. The widespread assumption that SMC extinction curves are more appropriate models for cosmological dust may be incorrect.
We present the results of a new study of dust attenuation at redshifts $3 < z < 4$ based on a sample of $236$ star-forming galaxies from the VANDELS spectroscopic survey. Motivated by results from the First Billion Years (FiBY) simulation project, we argue that the intrinsic spectral energy distributions (SEDs) of star-forming galaxies at these redshifts have a self-similar shape across the mass range $8.2 leq$ log$(M_{star}/M_{odot}) leq 10.6$ probed by our sample. Using FiBY data, we construct a set of intrinsic SED templates which incorporate both detailed star formation and chemical abundance histories, and a variety of stellar population synthesis (SPS) model assumptions. With this set of intrinsic SEDs, we present a novel approach for directly recovering the shape and normalization of the dust attenuation curve. We find, across all of the intrinsic templates considered, that the average attenuation curve for star-forming galaxies at $zsimeq3.5$ is similar in shape to the commonly-adopted Calzetti starburst law, with an average total-to-selective attenuation ratio of $R_{V}=4.18pm0.29$. We show that the optical attenuation ($A_V$) versus stellar mass ($M_{star}$) relation predicted using our method is consistent with recent ALMA observations of galaxies at $2<z<3$ in the emph{Hubble} emph{Ultra} emph{Deep} emph{Field} (HUDF), as well as empirical $A_V - M_{star}$ relations predicted by a Calzetti-like law. Our results, combined with other literature data, suggest that the $A_V - M_{star}$ relation does not evolve over the redshift range $0<z<5$, at least for galaxies with log$(M_{star}/M_{odot}) gtrsim 9.5$. Finally, we present tentative evidence which suggests that the attenuation curve may become steeper at log$(M_{star}/M_{odot}) lesssim 9.0$.
In this work, we study the properties of galaxies that are showing the inside-out assembly (which we call inside-out assembled galaxies; IOAGs), with the main aim to understand better their properties and morphological transformation. We analysed a sample of galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8), with stellar masses in the range $log M_{star}=10.73-11.03$ $M_{odot{}}$ at $z < 0.1$, and analyze their location in the stellar mass-SFR and the color-stellar mass diagram. We found that IOAGs have different spectroscopic properties, most of them being classified either as AGN or composite. We found that the majority of our sources are located below the main sequence of star formation in the SFR-stellar mass diagram, and in the green valley or red sequence in the color-stellar mass diagram. We argue that IOAGs seem to correspond to the transition area where the galaxies are moving from star-forming to quiescent, and from the blue cloud to the red sequence and/or to recently quenched galaxies.
We present the first measurements of the shape of the far-ultraviolet (far-UV; lambda=950-1500 A) dust attenuation curve at high redshift (z~3). Our analysis employs rest-frame UV spectra of 933 galaxies at z~3, 121 of which have very deep spectroscopic observations (>7 hrs) at lambda=850-1300 A, with the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an iterative approach in which we calculate the ratios of composite spectra in different bins of continuum color excess, E(B-V), we derive a dust curve that implies a lower attenuation in the far-UV for a given E(B-V) than those obtained with standard attenuation curves. We demonstrate that the UV composite spectra of z~3 galaxies can be modeled well by assuming our new attenuation curve, a high covering fraction of HI, and absorption from the Lyman-Werner bands of H2 with a small (<20%) covering fraction. The low covering fraction of H2 relative to that of the HI and dust suggests that most of the dust in the ISM of typical galaxies at z~3 is unrelated to the catalysis of H2, and is associated with other phases of the ISM (i.e., the ionized and neutral gas). The far-UV dust curve implies a factor of ~2 lower dust attenuation of Lyman continuum (ionizing) photons relative to those inferred from the most commonly assumed attenuation curves for L* galaxies at z~3. Our results may be utilized to assess the degree to which ionizing photons are attenuated in HII regions or, more generally, in the ionized or low column density (N(HI)<10^17.2 cm^-2) neutral ISM of high-redshift galaxies.
We present a novel approach to measure the attenuation curves of 485 individual star-forming galaxies with M$_*$ $>$ 10$^{10}$ M$_{odot}$ based on deep optical spectra from the VLT/VIMOS LEGA-C survey and multi-band photometry in the COSMOS field. Most importantly, we find that the attenuation curves in the rest-frame $3000-4500$A range are typically almost twice as steep as the Milky Way, LMC, SMC, and Calzetti attenuation curves, which is in agreement with recent studies of the integrated light of present-day galaxies. The attenuation at $4500$A and the slope strongly correlate with the galaxy inclination: face-on galaxies show less attenuation and steeper curves compared to edge-on galaxies, suggesting that geometric effects dominate observed variations in attenuation. Our new method produces $2175$A UV bump detections for 260 individual galaxies. Even though obvious correlations between UV bump strength and global galaxy properties are absent, strong UV bumps are most often seen in face-on, lower-mass galaxies (10 $<$ log$_{10}$(M$_*$/M$_{odot}$) $<$ 10.5) with low overall attenuation. Finally, we produce a typical attenuation curve for star-forming galaxies at $zsim0.8$; this prescription represents the effect of dust on the integrated spectral energy distributions of high-redshift galaxies more accurately than commonly used attenuation laws.
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