At low redshifts, dust-obscured quasars often have strong yet narrow permitted lines in the rest-frame optical and ultraviolet, excited by the central active nucleus, earning the designation type II ...quasars. We present a sample of 145 candidate type II quasars at redshifts between 2 and 4.3, encompassing the epoch at which quasar activity peaked in the universe. These objects, selected from the quasar sample of the Baryon Oscillation Spectroscopic Survey of the Sloan Digital Sky Survey III, are characterized by weak continuum in the rest-frame ultraviolet (typical continuum magnitude of i 22) and strong lines of C iv and Lyα, with full width at half-maximum less than 2000 km s−1. The continuum magnitudes correspond to an absolute magnitude of −23 or brighter at redshift 3, too bright to be due exclusively to the host galaxies of these objects. Roughly one third of the objects are detected in the shorter wavelength bands of the Wide-Field Infrared Survey Explorer survey; the spectral energy distributions of these objects appear to be intermediate between classic type I and type II quasars seen at lower redshift. Five objects are detected at rest frame 6 μm by Spitzer, implying bolometric luminosities of several times 1046 erg s−1. We have obtained polarization measurements for two objects; they are roughly 3 per cent polarized. We suggest that these objects are luminous quasars, with modest dust extinction (A
V
∼ 0.5 mag), whose ultraviolet continuum also includes a substantial scattering contribution. Alternatively, the line of sight to the central engines of these objects may be obscured by optically thick material whose covering fraction is less than unity.
ABSTRACT We present optical photometric and spectroscopic observations of SN 2013ej. It is one of the brightest Type II supernovae (SNe II) exploded in a nearby (∼10 Mpc) galaxy, NGC 628. The ...light-curve characteristics are similar to SNe II, but with a relatively shorter (∼85 days) and steeper (∼1.7 mag (100 days)−1 in V) plateau phase. The SN shows a large drop of 2.4 mag in V-band brightness during the plateau-to-nebular transition. The absolute ultraviolet (UV) light curves are identical to SN 2012aw, showing a similar UV-plateau trend extending up to 85 days. The radioactive 56Ni mass estimated from the tail luminosity is 0.02 , which is significantly lower than typical SNe IIP. The characteristics of spectral features and evolution of line velocities indicate that SN 2013ej is a Type II event. However, light-curve characteristics and some spectroscopic features provide strong support in classifying it as a Type IIL event. A detailed synow modeling of spectra indicates the presence of some high-velocity components in H and Hβ profiles, implying a possible ejecta-circumstellar medium interaction. The nebular phase spectrum shows an unusual notch in the H emission, which may indicate bipolar distribution of 56Ni. Modeling of the bolometric light curve yields a progenitor mass of ∼14 and a radius of ∼450 , with a total explosion energy of erg.
Abstract
We report Hubble Space Telescope Cosmic Origins Spectrograph spectroscopy of 10 quasars with foreground star-forming galaxies at 0.02 <
z
< 0.14 within impact parameters of ∼1–7 kpc. We ...detect damped/sub-damped Ly
α
(DLA/sub-DLA) absorption in 100% of cases where no higher-redshift Lyman-limit systems extinguish the flux at the expected wavelength of Ly
α
absorption, obtaining the largest targeted sample of DLA/sub-DLAs in low-redshift galaxies. We present absorption measurements of neutral hydrogen and metals. Additionally, we present Green Bank Telescope 21 cm emission measurements for five of the galaxies (including two detections). Combining our sample with the literature, we construct a sample of 117 galaxies associated with DLA/sub-DLAs spanning 0 <
z
< 4.4, and examine trends between gas and stellar properties, and with redshift. The H
i
column density is anticorrelated with impact parameter and stellar mass. More massive galaxies appear to have gas-rich regions out to larger distances. The specific star formation rate (sSFR) of absorbing galaxies increases with redshift and decreases with
M
*, consistent with evolution of the star formation main sequence (SFMS). However, ∼20% of absorbing galaxies lie below the SFMS, indicating that some DLA/sub-DLAs trace galaxies with longer-than-typical gas-depletion timescales. Most DLA/sub-DLA galaxies with 21 cm emission have higher H
i
masses than typical galaxies with comparable
M
*. High
M
HI
/
M
* ratios and high sSFRs in DLA/sub-DLA galaxies with
M
* < 10
9
M
⊙
suggest these galaxies may be gas-rich because of recent gas accretion rather than inefficient star formation. Our study demonstrates the power of absorption and emission studies of DLA/sub-DLA galaxies for extending galactic evolution studies to previously under-explored regimes of low
M
* and low SFR.
We discuss the thermal pressures (n sub(H)T) in predominantly cold, neutral interstellar gas in the Magellanic Clouds, derived from analyses of the fine-structure excitation of neutral carbon, as ...seen in high-resolution Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra of seven diverse sight lines in the LMC and SMC. Detailed fits to the line profiles of the absorption from C i, C i*, and C i** yield consistent column densities for the three to six C i multiplets detected in each sight line. In the LMC and SMC, N(C i sub(tot)) is consistent with Galactic trends versus N(Na i) and N(CH), but is slightly lower versus N(K i) and N(H sub(2)). As for N(Na i) and N(K i), N(C i sub(tot)) is generally significantly lower, for a given N(H sub(tot)), in the LMC and (especially) in the SMC, compared to the local Galactic relationship. For the LMC and SMC components with well-determined column densities for C i, C i*, and C i**, the derived thermal pressures are typically factors of a few higher than the values found for most cold, neutral clouds in the Galactic ISM. Such differences are consistent with the predictions of models for clouds in systems (like the LMC and SMC) that are characterized by lower metallicities, lower dust-to-gas ratios, and enhanced radiation fields-where higher pressures are required for stable cold, neutral clouds. The pressures may be further enhanced by energetic activity (e.g., due to stellar winds, star formation, and/or supernova remnants) in several of the regions probed by these sight lines. Comparisons are made with the C i observed in some quasar absorption-line systems.
We present a catalog of 5039 broad absorption line (BAL) quasars (QSOs) in the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) QSO catalog that have absorption troughs covering a continuous ...velocity range >=2000 km s-1. We have fitted ultraviolet (UV) continua and line emission in each case, enabling us to report common diagnostics of BAL strengths and velocities in the range -2,000 to 0 km s-1 for Si IV lambda 1400, C IV lambda 1549, Al III lambda 1857, and Mg II lambda 2799. We calculate these diagnostics using the spectrum listed in the DR5 QSO catalog, and also for spectra from additional SDSS observing epochs when available. In cases where BAL QSOs have been observed with Chandra or XMM-Newton, we report the X-ray monochromatic luminosities of these sources. We confirm and extend previous findings that BAL QSOs are more strongly reddened in the rest-frame UV than non-BAL QSOs, and that BAL QSOs are relatively X-ray weak compared to non-BAL QSOs. The observed BAL fraction is dependent on the spectral signal-to-noise ratio (S/N); for higher S/N sources, we find an observed BAL fraction of 15%. BAL QSOs show a similar Baldwin effect as for non-BAL QSOs, in that their C IV emission equivalent widths decrease with increasing continuum luminosity. However, BAL QSOs have weaker C IV emission in general than do non-BAL QSOs. Sources with higher UV luminosities are more likely to have higher-velocity outflows, and the BAL outflow velocity and UV absorption strength are correlated with relative X-ray weakness. These results are in qualitative agreement with models that depend on strong X-ray absorption to shield the outflow from overionization and enable radiative acceleration. In a scenario in which BAL trough shapes are primarily determined by outflow geometry, observed differences in Si IV and C IV trough shapes would suggest that some outflows have ion-dependent structure.
The use of background quasars provides a powerful tool to probe the cool gas in the circumgalactic medium of foreground galaxies. Here, we present new observations with SINFONI and X-Shooter of ...absorbing-galaxy candidates at z = 0.7–1. We report the detection with both instruments of the Hα emission line of one sub-damped Lyman α (sub-DLA) at z
abs = 0.941 87 with
$\log N({\rm H}\,{\small {I}})$
= 19.38
$^{+0.10}_{-0.15}$
towards SDSS J002133.27+004300.9. We estimate the star formation rate: SFR = 3.6 ± 2.2 M⊙ yr−1 in that system. A detailed kinematic study indicates a dynamical mass M
dyn = 109.9±0.4 M⊙ and a halo mass M
halo = 1011.9±0.5 M⊙. In addition, we report the O ii detection with X-Shooter of another DLA at z
abs = 0.7402 with
$\log N({\rm H}\,{\small {I}})$
= 20.4 ± 0.1 towards Q0052+0041 and an estimated SFR of 5.3 ± 0.7 M⊙ yr−1. Three other objects are detected in the continuum with X-Shooter but the nature and redshift of two of these objects are unconstrained due to the absence of emission lines, while the third object might be at the redshift of the quasar. We use the objects detected in our whole
$N({\rm H}\,{\small {I}})$
-selected SINFONI survey to compute the metallicity difference between the galaxy and the absorbing gas,
$\delta _{\rm H\,\small {I}}(X)$
, where a positive (negative) value indicates infall (outflow). We compare this quantity with the quasar line-of-sight alignment with the galaxy's major (minor) axis, another tracer of infall (outflow). We find that these quantities do not correlate as expected from simple assumptions. Additional observations are necessary to relate these two independent probes of gas flows around galaxies.
Abstract
We study the mean absorption spectrum of the Damped Ly
α
(DLA) population at
z
∼ 2.6 by stacking normalized, rest-frame-shifted spectra of ∼27,000 DLA systems from the DR12 of the Baryon ...Oscillation Spectroscopic Survey (BOSS)/SDSS-III. We measure the equivalent widths of 50 individual metal absorption lines in five intervals of DLA hydrogen column density, five intervals of DLA redshift, and overall mean equivalent widths for an additional 13 absorption features from groups of strongly blended lines. The mean equivalent width of low-ionization lines increases with
N
H
i
, whereas for high-ionization lines the increase is much weaker. The mean metal line equivalent widths decrease by a factor ∼1.1–1.5 from
z
∼ 2.1 to
z
∼ 3.5, with small or no differences between low- and high-ionization species. We develop a theoretical model, inspired by the presence of multiple absorption components observed in high-resolution spectra, to infer mean metal column densities from the equivalent widths of partially saturated metal lines. We apply this model to 14 low-ionization species and to Al
iii
, S
iii
, Si
iii
, C
iv
, Si
iv
, N
v,
and O
vi
. We use an approximate derivation for separating the equivalent width contributions of several lines to blended absorption features, and infer mean equivalent widths and column densities from lines of the additional species N
i
, Zn
ii
, C
ii
*, Fe
iii
, and S
iv
. Several of these mean column densities of metal lines in DLAs are obtained for the first time; their values generally agree with measurements of individual DLAs from high-resolution, high signal-to-noise ratio spectra when they are available.
Using the photometric parallax method we estimate the distances to similar to 48 million stars detected by the Sloan Digital Sky Survey (SDSS) and map their three-dimensional number density ...distribution in the Galaxy. The currently available data sample the distance range from 100 pc to 20 kpc and cover 6500 deg super(2) of sky, mostly at high Galactic latitudes ( degree 'b degree ' > 25). These stellar number density maps allow an investigation of the Galactic structure with no a priori assumptions about the functional form of its components. The data show strong evidence for a Galaxy consisting of an oblate halo, a disk component, and a number of localized overdensities. The number density distribution of stars as traced by M dwarfs in the solar neighborhood (D < 2 kpc) is well fit by two exponential disks (the thin and thick disk) with scale heights and lengths, bias corrected for an assumed 35% binary fraction, of H sub(1) = 300 pc and L sub(1) = 2600 pc, and H sub(2) = 900 pc and L sub(2) = 3600 pc, and local thick-to-thin disk density normalization P sub(thick) (R unk)/ unk (R unk) = 12%. we use the stars near main-sequence turnoff to measure the shape of the Galactic halo. We find a strong preference for oblate halo models, with best-fit axis ratio c/a = 0.64, PH proportional to r super(-2.8) power-law profile, and the local halo-to-thin disk normalization of 0.5%. Based on a series of Monte Carlo simulations, we estimate the errors of derived model parameters not to be larger than similar to 20% for the disk scales and similar to 10% for the density normalization, with largest contributions to error coming from the uncertainty in calibration of the photometric parallax relation and poorly constrained binary fraction. While generally consistent with the above model, the measured density distribution shows a number of statistically significant localized deviations. In addition to known features, such as the Monoceros stream, we detect two overdensities in the thick disk region at cylindrical galactocentric radii and heights (R, Z) similar to (6.5, 1.5) kpc and (R, Z) similar to (9.5, 0.8) kpc and a remarkable density enhancement in the halo covering over 1000 deg super(2) of sky toward the constellation of Virgo, at distances of similar to 6-20 kpc. Compared to counts in a region symmetric with respect to the l = 0 degree line and with the same Galactic latitude, the Virgo overdensity is responsible for a factor of 2 number density excess and may be a nearby tidal stream or a low-surface brightness dwarf galaxy merging with the Milky Way. The u-g color distribution of stars associated with it implies metallicity lower than that of thick disk stars and consistent with the halo metallicity distribution. After removal of the resolved overdensities, the remaining data are consistent with a smooth density distribution; we detect no evidence of further unresolved clumpy substructure at scales ranging from similar to 50 pc in the disk to similar to 1-2 kpc in the halo.
Abstract
We present the first results from a Hubble Space Telescope Wide Field Camera 3/Infrared program, which obtained direct imaging and grism observations of galaxies near quasar sightlines with ...a high frequency of uncorrelated foreground Mg
ii
absorption. These highly efficient observations targeted 54 Mg
ii
absorbers along the line of sight to nine quasars at
z
(qso
∼ 2. We find that 89% of the absorbers in the range of 0.64 <
z
< 1.6 can be spectroscopically matched to at least one galaxy with an impact parameter of less than 200 kpc and ∣Δ
z
∣/(1 +
z
) < 0.006. We have estimated the star formation rates and measured structural parameters for all detected galaxies with impact parameters in the range of 7–200 kpc and star formation rates greater than 1.3
M
⊙
yr
−1
. We find that galaxies associated with Mg
ii
absorption have significantly higher mean star formation rates and marginally higher mean star formation rate surface densities compared to galaxies with no detected Mg
ii
. Nearly half of the Mg
ii
absorbers match more than one galaxy, and the mean equivalent width of the Mg
ii
absorption is found to be greater for groups, compared to isolated galaxies. Additionally, we observe a significant redshift evolution in the physical extent of Mg
ii
-absorbing gas around galaxies and evidence of an enhancement of Mg
ii
within 50° of the minor axis, characteristic of outflows, which persists to 80 kpc around the galaxies, in agreement with recent predictions from simulations.
We report three additional Spectrograph for Integral Field Observations in the Near Infrared (SINFONI) detections of Hα emission line from quasar absorbers, two of which are new identifications. ...These were targeted among a sample of systems with
and metallicities measured from high-resolution spectroscopy. The detected galaxies are at impact parameters ranging from 6 to 12 kpc from the quasar's line of sight. We derive star formation rates (SFRs) of a few M⊙ yr−1 for the two absorbers at z
abs∼ 1 and SFR = 17 M⊙ yr−1 for the damped Lyman α system (DLA) at z
abs∼ 2. These three detections are found among a sample of 16 DLAs and sub-DLAs (five at z
abs∼ 1 and seven at z
abs∼ 2). For the remaining undetected galaxies, we derive flux limits corresponding to SFR < 0.1-11.0 M⊙ yr−1 depending on redshift of the absorber and depth of the data. When combined with previous results from our survey for galaxy counterparts to H i-selected absorbers, we find a higher probability of detecting systems with higher metallicity as traced by dust-free Zn/H metallicity. We also report a higher detection rate with SINFONI for host galaxies at z
abs∼ 1 than for systems at z
abs∼ 2. Using the N ii/Hα ratio, we can thus compare absorption and emission metallicities in the same high-redshift objects, more than doubling the number of systems for which such measures are possible.
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