arXiv subjects

Bahram Mobasher

Publications and source records attributed to Bahram Mobasher.

At least 217 records · Page 12Linked to original sources

arXiv2014

Rapid Decline of Lyman-alpha Emission Toward the Reionization Era

The observed deficit of strongly Lyman-alpha emitting galaxies at z>6.5 is attributed to either increasing neutral hydrogen in the intergalactic medium (IGM) and/or to the evolving galaxy properties. To investigate this, we have performed very deep near-IR spectroscopy of z>7 galaxies using MOSFIRE on the Keck-I Telescope. We measure the Lyman-alpha fraction at z~8 (combined photometric redshift peak at z=7.7) using two methods. First, we derived NLyα/Ntot directly using extensive simulations to correct for incompleteness. Second, we used a Bayesian formalism (introduced by Treu et al. 2012) that compares the z>7 galaxy spectra to models of the Lyman-alpha equivalent width (WLyα) distribution at z~6. We explored two simple evolutionary scenarios: smooth evolution where Lyman-alpha is attenuated in all galaxies by a constant factor (perhaps owing to processes from galaxy evolution or a slowly increasing IGM opacity), and patchy evolution where Lyman-alpha is blocked in some fraction of galaxies (perhaps due to the IGM being opaque along only some fraction of sightlines). The Bayesian formalism places stronger constraints compared with the direct method. Combining our data with that in the literature we find that at z~8 the Lyman-alpha fraction has dropped by a factor >3(84% confidence interval) using both the smooth and patchy scenarios compared to the z~6 values. Furthermore, we find a tentative evidence that the data favor the patchy scenario over smooth (with "positive" Bayesian evidence), extending trends observed at z~7 to higher redshift. If this decrease is a result of reionization as predicted by theory, then our data imply the volume averaged neutral hydrogen fraction in the IGM to be >0.3 suggesting that the reionization of the universe is in progress at z~8.

astro-ph.CO↗

arXiv2014

CANDELS/GOODS-S, CDFS, ECDFS: Photometric Redshifts For Normal and for X-Ray-Detected Galaxies

We present photometric redshifts and associated probability distributions for all detected sources in the Extended Chandra Deep Field South (ECDFS). The work makes use of the most up-to-date data from the Cosmic Assembly Near-IR Deep Legacy Survey (CANDELS) and the Taiwan ECDFS Near-Infrared Survey (TENIS) in addition to other data. We also revisit multi-wavelength counterparts for published X-ray sources from the 4Ms-CDFS and 250ks-ECDFS surveys, finding reliable counterparts for 1207 out of 1259 sources ($\sim 96\%$). Data used for photometric redshifts include intermediate-band photometry deblended using the TFIT method, which is used for the first time in this work. Photometric redshifts for X-ray source counterparts are based on a new library of AGN/galaxy hybrid templates appropriate for the faint X-ray population in the CDFS. Photometric redshift accuracy for normal galaxies is 0.010 and for X-ray sources is 0.014, and outlier fractions are $4\%$ and $5.4\%$ respectively. The results within the CANDELS coverage area are even better as demonstrated both by spectroscopic comparison and by galaxy-pair statistics. Intermediate-band photometry, even if shallow, is valuable when combined with deep broad-band photometry. For best accuracy, templates must include emission lines.

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arXiv2014

Kpc-scale Properties of Emission-line Galaxies

We perform a detailed study of the resolved properties of emission-line galaxies at kpc-scale to investigate how small-scale and global properties of galaxies are related. 119 galaxies with high-resolution Keck/DEIMOS spectra are selected to cover a wide range in morphologies over the redshift range 0.2<z<1.3. Using the HST/ACS and HST/WFC3 imaging data taken as a part of the CANDELS project, for each galaxy we perform SED fitting per resolution element, producing resolved rest-frame U-V color, stellar mass, star formation rate, age and extinction maps. We develop a technique to identify blue and red "regions" within individual galaxies, using their rest-frame color maps. As expected, for any given galaxy, the red regions are found to have higher stellar mass surface densities and older ages compared to the blue regions. Furthermore, we quantify the spatial distribution of red and blue regions with respect to both redshift and stellar mass, finding that the stronger concentration of red regions toward the centers of galaxies is not a significant function of either redshift or stellar mass. We find that the "main sequence" of star forming galaxies exists among both red and blue regions inside galaxies, with the median of blue regions forming a tighter relation with a slope of 1.1+/-0.1 and a scatter of ~0.2 dex compared to red regions with a slope of 1.3+/-0.1 and a scatter of ~0.6 dex. The blue regions show higher specific Star Formation Rates (sSFR) than their red counterparts with the sSFR decreasing since z~1, driver primarily by the stellar mass surface densities rather than the SFRs at a giver resolution element.

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arXiv2014

A Study of Massive and Evolved Galaxies at High Redshift

We use data taken as part of HST/WFC3 observations of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) to identify massive and evolved galaxies at 3<z<4.5. This is performed using the strength of the Balmer break feature at rest-frame 3648A, which is a diagnostic of the age of the stellar population in galaxies. Using WFC3 H-band selected catalog for the CANDELS GOODS-S field and deep multi-waveband photometry from optical (HST) to mid-infrared (Spitzer) wavelengths, we identify a population of old and evolved post-starburst galaxies based on the strength of their Balmer breaks (Balmer Break Galaxies- BBGs). The galaxies are also selected to be bright in rest-frame near-IR wavelengths and hence, massive. We identify a total of 16 BBGs. Fitting the spectral energy distribution (SED) of the BBGs show that the candidate galaxies have average estimated ages of ~800 Myr and average stellar masses of ~5x10^10 M_sun, consistent with being old and massive systems. Two of our BBG candidates are also identified by the criteria that is sensitive to star forming galaxies (LBG selection). We find a number density of ~3.2x10^-5 Mpc^-3 for the BBGs corresponding to a mass density of ~2.0x10^6 M_sun/Mpc^3 in the redshift range covering the survey. Given the old age and the passive evolution, it is argued that some of these objects formed the bulk of their mass only a few hundred million years after the Big Bang.

astro-ph.GA↗

arXiv2014

The HST/ACS Coma Cluster Survey - VII. Structure and Assembly of Massive Galaxies in the Center of the Coma Cluster

We constrain the assembly history of galaxies in the projected central 0.5 Mpc of the Coma cluster by performing structural decomposition on 69 massive (M_star >= 10^9 M_sun) galaxies using high-resolution F814W images from the HST Treasury Survey of Coma. Each galaxy is modeled with up to three Sersic components having a free Sersic index n. After excluding the two cDs in the projected central 0.5 Mpc of Coma, 57% of the galactic stellar mass in the projected central 0.5 Mpc of Coma resides in classical bulges/ellipticals while 43% resides in cold disk-dominated structures. Most of the stellar mass in Coma may have been assembled through major (and possibly minor) mergers. Hubble types are assigned based on the decompositions, and we find a strong morphology-density relation; the ratio of (E+S0):spirals is (91.0%):9.0%. In agreement with earlier work, the size of outer disks in Coma S0s/spirals is smaller compared with lower-density environments captured with SDSS (Data Release 2). Among similar-mass clusters from a hierarchical semi-analytic model, no single cluster can simultaneously match all the global properties of the Coma cluster. The model strongly overpredicts the mass of cold gas and underpredicts the mean fraction of stellar mass locked in hot components over a wide range of galaxy masses. We suggest that these disagreements with the model result from missing cluster physics (e.g., ram-pressure stripping), and certain bulge assembly modes (e.g., mergers of clumps). Overall, our study of Coma underscores that galaxy evolution is not solely a function of stellar mass, but also of environment.

astro-ph.CO↗

arXiv2014

Type Ia Supernova Rate Measurements to Redshift 2.5 from CANDELS : Searching for Prompt Explosions in the Early Universe

The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was a multi-cycle treasury program on the Hubble Space Telescope (HST) that surveyed a total area of ~0.25 deg^2 with ~900 HST orbits spread across 5 fields over 3 years. Within these survey images we discovered 65 supernovae (SN) of all types, out to z~2.5. We classify ~24 of these as Type Ia SN (SN Ia) based on host-galaxy redshifts and SN photometry (supplemented by grism spectroscopy of 6 SN). Here we present a measurement of the volumetric SN Ia rate as a function of redshift, reaching for the first time beyond z=2 and putting new constraints on SN Ia progenitor models. Our highest redshift bin includes detections of SN that exploded when the universe was only ~3 Gyr old and near the peak of the cosmic star-formation history. This gives the CANDELS high-redshift sample unique leverage for evaluating the fraction of SN Ia that explode promptly after formation (<500 Myr). Combining the CANDELS rates with all available SN Ia rate measurements in the literature we find that this prompt SN Ia fraction is fP=0.53 +0.09 -0.10 (stat) +0.10 -0.26 (sys), consistent with a delay time distribution that follows a simple t^{-1} power law for all times t>40 Myr. However, a mild tension is apparent between ground-based low-z surveys and space-based high-z surveys. In both CANDELS and the sister HST program CLASH, we find a low rate of SN Ia at z>1. This could be a hint that prompt progenitors are in fact relatively rare, accounting for only ~20% of all SN Ia explosions -- though further analysis and larger samples will be needed to examine that suggestion.

astro-ph.CO↗

arXiv2014

Properties of Submillimeter Galaxies in the CANDELS GOODS-S Field

We derive physical properties of 10 submillimeter galaxies located in the CANDELS coverage of the GOODS-S field. The galaxies were first identified as submillimeter sources with the LABOCA bolometer and subsequently targeted for 870um continuum observation with ALMA. The high angular resolution of the ALMA imaging allows secure counterparts to be identified in the CANDELS multiband dataset. The CANDELS data provide deep photometric data from UV through near-infrared wavelengths. Using synthetic spectral energy distributions, we derive photometric redshifts, stellar masses, extinction, ages, and the star formation history. The redshift range is z=1.65-4.76, with two of the galaxies located at z>4. Two SMG counterparts have stellar masses 2-3 orders of magnitude lower than the rest. The remaining SMG counterparts have stellar masses around 1x10^11 Msun. The stellar population in the SMGs is typically older than the expected duration of the submillimeter phase, suggesting that the star formation history of submillimeter galaxies is more complex than a single burst. Non-parametric morphology indices suggest that the SMG counterparts are among the most asymmetric systems compared with galaxies of the same stellar mass and redshift. The HST images shows that 3 of the SMGs are associated with on-going mergers. The remaining counterparts are isolated. Estimating the dust and molecular gas mass from the submm fluxes, and comparing with our stellar masses shows that the molecular gas mass fraction of SMGs is ~28% and that the final stellar mass is likely to be (1-2)x10^11 Msun.

astro-ph.GA↗

arXiv2014

Physical Properties of Emission-Line Galaxies at z ~ 2 from Near-Infrared Spectroscopy with Magellan FIRE

We present results from near-infrared spectroscopy of 26 emission-line galaxies at z ~ 2 obtained with the FIRE spectrometer on the Magellan Baade telescope. The sample was selected from the WISP survey, which uses the near-infrared grism of the Hubble Space Telescope Wide Field Camera 3 to detect emission-line galaxies over 0.3 < z < 2.3. Our FIRE follow-up spectroscopy (R~5000) over 1.0-2.5 micron permits detailed measurements of physical properties of the z~2 emission-line galaxies. Dust-corrected star formation rates for the sample range from ~5-100 M_sun yr-1. We derive a median metallicity for the sample of ~0.45 Z_sun, and the estimated stellar masses range from ~10^8.5 - 10^9.5 M_sun. The average ionization parameters measured for the sample are typically much higher than what is found for local star-forming galaxies. We derive composite spectra from the FIRE sample, from which we infer typical nebular electron densities of ~100-400 cm^-3. Based on the location of the galaxies and composite spectra on BPT diagrams, we do not find evidence for significant AGN activity in the sample. Most of the galaxies as well as the composites are offset in the BPT diagram toward higher [O III]/H-beta at a given [N II]/H-alpha, in agreement with other observations of z > 1 star-forming galaxies, but composite spectra derived from the sample do not show an appreciable offset from the local star-forming sequence on the [O III]/H-beta versus [S II]/H-alpha diagram. We infer a high nitrogen-to-oxygen abundance ratio from the composite spectrum, which may contribute to the offset of the high-redshift galaxies from the local star-forming sequence in the [O III]/H-beta versus [N II]/H-alpha diagram. We speculate that the elevated nitrogen abundance could result from substantial numbers of Wolf-Rayet stars in starbursting galaxies at z~2. (Abridged)

astro-ph.GA↗

arXiv2013

The dependency of AGN infrared color-selection on source luminosity and obscuration: An observational perspective in CDFS and COSMOS

AIMS. This work addresses the AGN IR-selection dependency on intrinsic source luminosity and obscuration, in order to identify and charaterise biases which could affect conclusions in studies. METHODS. We study IR-selected AGN in the Chandra Deep Field South (CDFS) survey and in the Cosmological Survey (COSMOS). The AGN sample is divided into low and high X-ray luminosity classes, and into unobscured (type-1) and obscured (type-2) classes by means of X-ray and optical spectroscopy data. Specifically in the X-rays regime, we adopt the intrinsic luminosity taking into account the estimated column density (N_H). We also take the chance to highlight important differences resulting from adopting different methods to assess AGN obscuration. RESULTS. In agreement with previous studies, we also find that AGN IR-selection efficiency shows a decrease with decreasing source AGN X-ray luminosity. For the intermediate-luminosity AGN population (43.3<~log(L_X[erg/s])<~44$), the efficiency also worsens with increasing obscuration. The same sample also shows an evolution with cosmic time of the obscured fraction at the highest X-ray luminosities, independently of adopted type-1/type-2 classification method. CONCLUSIONS. We confirm that AGN IR-selection is genuinely biased toward unobscured AGN, but only at intermediate luminosities. At the highest luminosities, where AGN IR-selection is more efficient, there is no obscuration bias. We show that type-1 AGN are intrinsically more luminous than type-2 AGN only at z<~1.6, thus resulting in more type-1 AGN being selected the shallower the IR survey is. [ABRIDGED: Conclusion on survey strategy. See manuscript.] Finally, when the James Webb Space Telescope comes online, the broad-band filters 2.0um, 4.4um, 7.7um, and 18um will be key to disentangle AGN from non-AGN dominated SEDs at depths where spectroscopy becomes impractical.

astro-ph.GA↗

arXiv2013

The stellar mass function of star-forming galaxies and the mass-dependent SFR function since z=2.23 from HiZELS

We explore a large uniformly selected sample of H$α$ selected star-forming galaxies (SFGs) at z=0.40,0.84,1.47,2.23 to unveil the evolution of the star formation rate (SFR) function and the stellar mass function. We find strong evolution in the SFR function, with the typical SFR of SFGs declining exponentially with time in the last 11Gyrs as SFR$^*$(T[Gyr])=10$^{4.23/T+0.37}$ M$_{\odot}$yr$^{-1}$, but with no evolution in the faint-end slope, $α\approx$-1.6. The stellar mass function of SFGs, however, reveals little evolution: $α \approx$-1.4, M$^*$$\approx$10$^{11.2\pm0.2}$ M$_{\odot}$ and just a slight increase of $\approx$2.3x in $Φ^*$ from z=2.23 to z=0.4. The stellar mass density within SFGs has been roughly constant since z=2.23 at $\approx$10$^{7.65\pm0.08}$ M$_{\odot}$Mpc$^{-3}$, comprising $\approx$100% of the stellar mass density in all galaxies at z=2.23, and declining to $\approx$20% by z=0.4, driven by the rise of the passive population. We find that SFGs with M$\approx$10$^{10.0\pm0.2}$ M$_{\odot}$ contribute most to the SFR density ($ρ_{\rm SFR}$) per dlog$_{10}$M, and that there is no significant evolution in the fractional contribution from SFGs of different masses to $ρ_{\rm SFR}$ or $ρ_{\rm SFR}$(dlog$_{10}$M)$^{-1}$ since z=2.23. Instead, we show that the decline of SFR$^*$ and of $ρ_{\rm SFR}$ are primarily driven by an exponential decline in SFRs at all masses. Our results have important implications not only on how SFGs need to be quenched across cosmic time, but also on the driver(s) of the exponential decline in SFR$^*$ from $\approx$66 M$_{\odot}$yr$^{-1}$ to $\approx$5 M$_{\odot}$yr$^{-1}$ since z=2.23.

astro-ph.CO↗

arXiv2013

A Critical Assessment of Photometric Redshift Methods: A CANDELS Investigation

We present results from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) photometric redshift methods investigation. In this investigation, the results from eleven participants, each using a different combination of photometric redshift code, template spectral energy distributions (SEDs) and priors, are used to examine the properties of photometric redshifts applied to deep fields with broad-band multi-wavelength coverage. The photometry used includes U-band through mid-infrared filters and was derived using the TFIT method. Comparing the results, we find that there is no particular code or set of template SEDs that results in significantly better photometric redshifts compared to others. However, we find codes producing the lowest scatter and outlier fraction utilize a training sample to optimize photometric redshifts by adding zero-point offsets, template adjusting or adding extra smoothing errors. These results therefore stress the importance of the training procedure. We find a strong dependence of the photometric redshift accuracy on the signal-to-noise ratio of the photometry. On the other hand, we find a weak dependence of the photometric redshift scatter with redshift and galaxy color. We find that most photometric redshift codes quote redshift errors (e.g., 68% confidence intervals) that are too small compared to that expected from the spectroscopic control sample. We find that all codes show a statistically significant bias in the photometric redshifts. However, the bias is in all cases smaller than the scatter, the latter therefore dominates the errors. Finally, we find that combining results from multiple codes significantly decreases the photometric redshift scatter and outlier fraction. We discuss different ways of combining data to produce accurate photometric redshifts and error estimates.

astro-ph.CO↗

arXiv2013

Hot-Dust (690K) Luminosity Density and its Evolution in the last 7.5Gyr

[Abridged] We study the contribution of hot-dust to the luminosity density of galaxies and its evolution with cosmic time. Using the Spitzer-IRAC data in the COSMOS field, we estimate the contribution from hot-dust at rest-frame 4.2um (from ~0 < z < ~0.2 up to ~0.5 < z < ~0.9). This wavelength corresponds to black-body temperature of ~690K. The contribution due to stellar emission is estimated from the rest-frame 1.6um luminosity (assumed to result from stellar emission alone) and subtracted from the mid-infrared luminosity of galaxies to measure hot-dust emission. In order to attempt the study of the 3.3um-PAH feature, we use the rest-frame 4.2um to infer the hot-dust flux at 3.3um. This study is performed for different spectral types of galaxies: early-type, late-type, starburst, and IR-selected AGN. We find that: (a) the decrease of the hot-dust luminosity density since ~0.5 < z < ~1 is steeper (by at least ~0.5dex) compared to that of the cold-dust, giving support to the scenario where galaxy obscuration increases with redshift, as already proposed in the literature; (b) hot-dust and PAH emission evolution seems to be correlated with stellar mass, where rest-frame 1.6um luminous non-AGN galaxies (i.e., massive systems) show a stronger decrement (with decreasing redshift) in hot-dust and PAH emission than the less luminous (less massive) non-AGN galaxies; (c) despite comprising < ~3% of the total sample, AGN contribute as much as a third to the hot-dust luminosity density at z < 1 and clearly dominate the bright-end of the total hot-dust Luminosity Density Function at ~0.5 < z < ~0.9; (d) the average dust-to-total luminosity ratio increases with redshift, while PAH-to-total luminosity ratio remains fairly constant; (e) at M_1.6 > -25, the dust-to-total and PAH-to-total luminosity ratios increase with decreasing luminosity, but deeper data is required to confirm this result.

astro-ph.CO↗

arXiv2013

CANDELS Multi-wavelength Catalogs: Source Detection and Photometry in the GOODS-South Field

We present a UV-to-mid infrared multi-wavelength catalog in the CANDELS/GOODS-S field, combining the newly obtained CANDELS HST/WFC3 F105W, F125W, and F160W data with existing public data. The catalog is based on source detection in the WFC3 F160W band. The F160W mosaic includes the data from CANDELS deep and wide observations as well as previous ERS and HUDF09 programs. The mosaic reaches a 5$σ$ limiting depth (within an aperture of radius 0.17 arcsec) of 27.4, 28.2, and 29.7 AB for CANDELS wide, deep, and HUDF regions, respectively. The catalog contains 34930 sources with the representative 50% completeness reaching 25.9, 26.6, and 28.1 AB in the F160W band for the three regions. In addition to WFC3 bands, the catalog also includes data from UV (U-band from both CTIO/MOSAIC and VLT/VIMOS), optical (HST/ACS F435W, F606W, F775W, F814W, and F850LP), and infrared (HST/WFC3 F098M, VLT/ISAAC Ks, VLT/HAWK-I Ks, and Spitzer/IRAC 3.6, 4.5, 5.8, 8.0 $μ$m) observations. The catalog is validated via stellar colors, comparison with other published catalogs, zeropoint offsets determined from the best-fit templates of the spectral energy distribution of spectroscopically observed objects, and the accuracy of photometric redshifts. The catalog is able to detect unreddened star-forming (passive) galaxies with stellar mass of 10^{10}M_\odot at a 50% completeness level to z$\sim$3.4 (2.8), 4.6 (3.2), and 7.0 (4.2) in the three regions. As an example of application, the catalog is used to select both star-forming and passive galaxies at z$\sim$2--4 via the Balmer break. It is also used to study the color--magnitude diagram of galaxies at 0<z<4.

astro-ph.CO↗

arXiv2013

The Discovery of the Most Distant Known Type Ia Supernova at Redshift 1.914

We present the discovery of a Type Ia supernova (SN) at redshift $z = 1.914$ from the CANDELS multi-cycle treasury program on the \textit{Hubble Space Telescope (HST)}. This SN was discovered in the infrared using the Wide-Field Camera 3, and it is the highest-redshift Type Ia SN yet observed. We classify this object as a SN\,Ia by comparing its light curve and spectrum with those of a large sample of Type Ia and core-collapse supernovae (SNe). Its apparent magnitude is consistent with that expected from the $Λ$CDM concordance cosmology. We discuss the use of spectral evidence for classification of $z > 1.5$ SNe\,Ia using {\it HST} grism simulations, finding that spectral data alone can frequently rule out SNe\,II, but distinguishing between SNe\,Ia and SNe\,Ib/c can require prohibitively long exposures. In such cases, a quantitative analysis of the light curve may be necessary for classification. Our photometric and spectroscopic classification methods can aid the determination of SN rates and cosmological parameters from the full high-redshift CANDELS SN sample.

astro-ph.CO↗

arXiv2012

The Dwarf Starburst Host Galaxy of a Type Ia SN at z = 1.55 from CANDELS

We present VLT/X-shooter observations of a high redshift, type Ia supernova host galaxy, discovered with HST/WFC3 as part of the CANDELS Supernova project. The galaxy exhibits strong emission lines of Lyα, [O II], Hβ, [O III], and Hα at z = 1.54992(+0.00008-0.00004). From the emission-line fluxes and SED fitting of broad-band photometry we rule out AGN activity and characterize the host galaxy as a young, low mass, metal poor, starburst galaxy with low intrinsic extinction and high Lyα escape fraction. The host galaxy stands out in terms of the star formation, stellar mass, and metallicity compared to its lower redshift counterparts, mainly because of its high specific star-formation rate. If valid for a larger sample of high-redshift SN Ia host galaxies, such changes in the host galaxy properties with redshift are of interest because of the potential impact on the use of SN Ia as standard candles in cosmology.

astro-ph.CO↗

arXiv2012

SDSS 0956+5128: A Broad-line Quasar with Extreme Velocity Offsets

We report on the discovery of a Type 1 quasar, SDSS 0956+5128, with a surprising combination of extreme velocity offsets. SDSS 0956+5128 is a broad-lined quasar exhibiting emission lines at three substantially different redshifts: a systemic redshift of z ~ 0.714 based on narrow emission lines, a broad MgII emission line centered 1200 km/s bluer than the systemic velocity, at z ~ 0.707, and broad Hαand Hβemission lines centered at z ~ 0.690. The Balmer line peaks are 4100 km/s bluer than the systemic redshift. There are no previously known objects with such an extreme difference between broad MgII and broad Balmer emission. The two most promising explanations are either an extreme disk emitter or a high-velocity black hole recoil. However, neither explanation appears able to explain all of the observed features of SDSS 0956+5128, so the object may provide a challenge to our general understanding of quasar physics.

astro-ph.HE↗

arXiv2012

The Extended Hubble Space Telescope Supernova Survey: The Rate of Core Collapse Supernovae to z~1

We use a sample of 45 core collapse supernovae detected with the Advanced Camera for Surveys on-board the Hubble Space Telescope to derive the core collapse supernova rate in the redshift range 0.1 =0.39, =0.73, and =1.11, we find rates 3.00 {+1.28}{-0.94}{+1.04}{-0.57}, 7.39 {+1.86}{-1.52}{+3.20}{-1.60}, and 9.57 {+3.76}{-2.80}{+4.96}{-2.80}, respectively, given in units yr^{-1} Mpc^{-3} 10^{-4} h_{70}^3. The rates have been corrected for host galaxy extinction, including supernovae missed in highly dust enshrouded environments in infrared bright galaxies. The first errors represent statistical while the second are the estimated systematic errors. We perform a detailed discussion of possible sources of systematic errors and note that these start to dominate over statistical errors at z>0.5, emphasizing the need to better control the systematic effects. For example, a better understanding of the amount of dust extinction in the host galaxies and knowledge of the supernova luminosity function, in particular the fraction of faint M > -15 supernovae, is needed to better constrain the rates. When comparing our results with the core collapse supernova rate based on the star formation rate, we find a good agreement, consistent with the supernova rate following the star formation rate, as expected.

astro-ph.CO↗

arXiv2012

Lyα Emission from High Redshift Sources in COSMOS

We investigate spectroscopically measured Lyα equivalent widths and escape fractions of 244 sources of which 95 are Lyman Break Galaxies (LBGs) and 106 Lyman Alpha Emitters (LAEs) at z~4.2, z~4.8, and z~5.6 selected from intermediate and narrow band observations. The sources were selected from the Cosmic Evolution Survey (COSMOS), and observed with the DEIMOS spectrograph. We find that the distribution of equivalent widths shows no evolution with redshift for both the LBG selected sources and the intermediate/narrowband LAEs. We also find that the Lyα escape fraction of intermediate and narrow band LAEs is on average higher and has a larger variation than the escape fraction of LBG selected sources. The escape fraction does not show a dependence with redshift. Similar to what has been found for LAEs at low redshifts, the sources with the highest extinctions show the lowest escape fractions. The range of escape fractions increases with decreasing extinction. This is evidence that the dust extinction is the most important factor affecting the escape of Lyα photons, but at low extinctions other factors such as HI covering fraction and gas kinematics can be just as effective at inhibiting the escape of Lyα photons.

astro-ph.CO↗