- ID:
- ivo://CDS.VizieR/J/ApJ/475/469
- Title:
- Composite HST Spectrum of Quasars
- Short Name:
- J/ApJ/475/469
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct a composite quasar spectrum from 284 HST FOS spectra of 101 quasars with redshifts z>0.33. The spectrum covers the wavelengths between 350 and 3000A in the rest frame, with a peak S/N level of ~130 per A at ~1200A. Since ~90% of the sample quasars have redshift z<1.5, the spectrum is suitable for studying the wavelength region shortward of Ly{alpha} without large effects from intervening Ly{alpha} forest absorption. Data in the waveband between 350 and 600A are mainly from the spectra of z>1.5 quasars, for which significant corrections for the accumulated Lyman-series line and continuum absorption have been applied. There is a significant steepening of the continuum slope around 1050A. The continuum between 1050 and 2200A can be modeled as a power law f_{nu} proportional to {nu}_{alpha}_ with {alpha}=-0.99+/-0.05. For the full sample the power-law index in the extreme ultraviolet (EUV) between 350 and 1050A is {alpha}=-1.96+/-0.15. For the radio-loud subsample (60 objects), the EUV spectral index is {alpha}~=-2.2, while for the radio-quiet subsample (41 objects) it is {alpha}~=-1.8. The continuum flux in the wavelengths near the Lyman limit shows a depression of ~10%. The break in the power-law index and the slight depression of the continuum near the Lyman limit are features expected in Comptonized accretion-disk spectra. Comptonization produces a power-law tail in the wavelength band shortward of 1000A and smears out the Lyman-limit edge of the intrinsic accretion-disk spectrum. In the EUV waveband, we detect several possible emission features, including one around 690A that may be O III + N III produced by the Bowen fluorescence effect. Comparing our composite spectrum with one made at higher redshifts by Francis et al. (1991ApJ...373..465F), we find that the equivalent widths of Ly{alpha} and high-ionization emission lines are larger in our sample, reflecting a known luminosity dependence. The equivalent widths of low-ionization lines do not exhibit such a dependence, suggesting that the quasar EUV continuum above ~50eV is steeper at higher luminosity. Radio-quiet quasars appear to show a slightly harder continuum and lower ionization levels in their emission lines.
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- ID:
- ivo://CDS.VizieR/J/ApJ/551/111
- Title:
- HDF early-type and spiral galaxies
- Short Name:
- J/ApJ/551/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the internal optical colors of a complete sample of I_814_<24mag early-type and spiral galaxies from the northern and southern Hubble Deep Fields (HDF). The subset of galaxies in the HDF-North are also investigated in the near-infrared using NICMOS photometry. We compare the central (inner 5% radius) colors of those spirals with clearly visible bulges with the integrated colors of ellipticals in our sample.
- ID:
- ivo://CDS.VizieR/J/A+A/364/517
- Title:
- HDF-N spiral and irregular galaxies
- Short Name:
- J/A+A/364/517
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a morphologically-selected complete sample of 52 late-type (spiral and irregular) galaxies in the Hubble Deep Field North with total K-magnitudes brighter than K=20.47 and typical redshifts z~0.5 to 1.4. This sample exploits in particular the ultimate imaging quality achieved by HST in this field, allowing us to clearly disentangle the early- from late-type galaxy morphologies, based on accurate profiles of the surface brightness distributions.
- ID:
- ivo://CDS.VizieR/J/ApJ/513/34
- Title:
- HDF photometric redshifts catalog
- Short Name:
- J/ApJ/513/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the newly available infrared images of the Hubble Deep Field in the J, H, and K bands and an optimal photometric method, we have refined a technique to estimate the redshifts of 1067 galaxies. A detailed comparison of our results with the spectroscopic redshifts in those cases where the latter are available shows that this technique gives very good results for bright enough objects [AB(814nm)<26.0]. From a study of the distribution of residuals [{Delta}z_rms_/(1+z)~0.1 at all redshifts], we conclude that the observed errors are mainly due to cosmic variance. This very important result allows for the assessment of errors in quantities to be directly or indirectly measured from the catalog. We present some of the statistical properties of the ensemble of galaxies in the catalog, and we finish by presenting a list of bright high-redshift (z~5) candidates extracted from our catalog together with recent spectroscopic redshift determinations confirming that two of them are at z=5.34 and z=5.60.
- ID:
- ivo://CDS.VizieR/J/ApJ/538/493
- Title:
- HDF-South NICMOS field
- Short Name:
- J/ApJ/538/493
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of photometry and photometric redshifts of 335 faint objects in the Hubble Deep Field South (HDF-S) near-infrared camera and multiobject spectrograph (NICMOS) field. The analysis is based on (1) infrared images obtained with the Hubble Space Telescope (HST) using the NICMOS with the F110W, F160W, and F222M filters; (2) an optical image obtained with HST using the Space Telescope Imaging Spectrograph with no filter; and (3) optical images obtained with the European Southern Observatory Very Large Telescope with U, B, V, R, and I filters. The primary utility of the catalog of photometric redshifts is as a survey of faint galaxies detected in the NICMOS F160W and F222M images. The sensitivity of the survey varies significantly with position, reaching a limiting depth of AB(1.6{mu}m)~28.7 and covering 1.01arcmin^2^ to AB(1.6{mu}m)=27 and 1.05arcmin^2^ to AB(1.6{mu}m)=26.5. The catalog of photometric redshifts identifies 21 galaxies (or 6% of the total) of redshift z>5, eight galaxies (or 2% of the total) of redshift z>10, and 11 galaxies (or 3% of the total) of best-fit spectral type E/S0, of which five galaxies (or 1% of the total) are of redshift z>1.
- ID:
- ivo://CDS.VizieR/J/ApJ/499/112
- Title:
- HST CFRS and LDSS redshift surveys. I.
- Short Name:
- J/ApJ/499/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze Hubble Space Telescope images of a complete sample of 341 galaxies drawn from the Canada-France Redhsift Survey (CFRS) and Low-Dispersion Survey Spectrograph (LDSS) ground-based redshift surveys. In this, the first paper in the series, each galaxy has been morphologically classified according to a scheme similar to that developed for the Medium Deep Survey. We discuss the reproducibility of these classifications and quantify possible biases that may arise from various redshift-dependent effects. We then discuss automated classifications of the sample and conclude, from several tests, that we can expect an apparent migration with redshift to later Hubble types that corresponds to a misclassification in our adopted machine classification system of ~24%+/-11 of the true "spirals" as "peculiars" at a redshift z~=0.9. After allowing for such biases, the redshift distribution for normal spirals, together with their luminosity function derived as a function of redshift, indicates approximately 1mag of luminosity evolution in B_AB_ by z~=1. The elliptical sample is too small for precise evolutionary constraints. However, we find a substantial increase in the proportion of galaxies with irregular morphology at large redshift from 9%+/-3% for 0.3<=z<=0.5 to 32%+/-12% for 0.7<=z<=0.9. These galaxies also appear to be the dominant cause of the rapid rise with redshift in the blue luminosity density identified in the redshift surveys. Although galaxies with irregular morphology may well comprise a mixture of different physical systems and might not correspond to present-day irregulars, it is clear that the apparently declining abundance and luminosities of our distant "irregulars" holds an important key to understanding recent evolution in the star formation history of normal galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJS/97/1
- Title:
- HST Quasar Absorption Line Key Project. X.
- Short Name:
- J/ApJS/97/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Sensitive H I 21cm emission line spectra have been measured for the directions to 143 quasars and AGNs chosen from the observing lists for the HST Quasar Absorption Line Key Project. Narrow-band and wide-band data were obtained with the NRAO 43m radio telescope for each object. The narrow-band data have a velocity resolution of 1km/s, extend from -220 to +170km/s, and are corrected for stray 21cm radiation. The wide-band data have a resolution of 4km/s and extend from -1000 to +1000km/s. The data are important for the interpretation of ultraviolet absorption lines near zero redshift in Key Project spectra. Twenty-two percent of the quasars lie behind Galactic high-velocity H I clouds with |VLSR|>100km/s whose presence can increase the equivalent width of interstellar absorption lines significantly. This paper contains the emission spectra and measures of the H I velocities and column densities along the sight line to each quasar. We discuss how the measurements can be used to estimate the visual and ultraviolet extinction toward each quasar and to predict the approximate strength of the strong ultraviolet resonance lines of neutral gas species in the HST Key Project spectra.
- ID:
- ivo://CDS.VizieR/J/AJ/116/2081
- Title:
- Hubble Deep Field catalog of color-based redshift
- Short Name:
- J/AJ/116/2081
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive simple empirical color-redshift relations for z<~4 galaxies in the Hubble Deep Field (HDF) using a linear function of three photometric colors (U-B, B-V, V-I). The dispersion between the estimated redshifts and the spectroscopically observed ones is small for relations derived in several separate color regimes; the dispersions range from {sigma}_z_~=0.03 to 0.1 for z<~2 galaxies, and from {sigma}_z_~=0.14 to 0.25 for z>~2 galaxies. We apply the color-redshift relations to the HDF photometric catalog and obtain estimated redshifts that are consistent with those derived from spectral template fitting methods. The advantage of these color-redshift relations is that they are simple and easy to use and do not depend on the assumption of any particular spectral templates; they provide model independent redshift estimates for z<~4 galaxies using only multiband photometry, and they apply to about 90% of all galaxies. We provide a color-based estimated redshift catalog of HDF galaxies to z<~4. We use the estimated redshifts to investigate the redshift distribution of galaxies in the HDF; we find peaks in the redshift distribution that suggest large-scale clustering of galaxies to at least z~1 and that are consistent with those identified in spectroscopic probes of the HDF.
- ID:
- ivo://CDS.VizieR/J/ApJ/596/748
- Title:
- IR Observations in HDF-North
- Short Name:
- J/ApJ/596/748
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The original analysis of the star formation history in the NICMOS deep images of the northern Hubble Deep Field (NHDF) is extended to the entire NHDF utilizing NICMOS and WFPC2 archival data. The roughly constant star formation rate from redshifts 16 found in this study is consistent with the original results. Star formation rates from this study, Lyman break galaxies, and submillimeter observations are now in concordance. The spike of star formation at redshift 2 due to two ultraluminous IR galaxies in the small deep NICMOS field is smoothed out in the larger area results presented here. The larger source base of this study allows comparison with predictions from hierarchical galaxy formation models. In general, the observation are consistent with the predictions. The observed luminosity functions at redshifts 16 are presented for future comparisons with theoretical galaxy evolution calculations. Mid- and far-infrared properties of the sources are also calculated and compared with observations. A candidate for the VLA source VLA 3651+1221 is discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/546/694
- Title:
- NICMOS star formation history
- Short Name:
- J/ApJ/546/694
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an extensive analysis of the star formation rates determined from the NICMOS deep images of the northern Hubble Deep Field. We use SED template fitting photometric techniques to determine both the redshift and the extinction for each galaxy in our field. Measurement of the individual extinctions provides a correction for star formation hidden by dust obscuration. We determine star formation rates for each galaxy based on the 1500{AA} UV flux and add the rates in redshift bins of width 1.0 centered on integer redshift values.
