We introduce a data set of 142 mostly late-type spiral, irregular, and peculiar (interacting or merging) nearby galaxies observed in UBVR at the Vatican Advanced Technology Telescope (VATT), and we ...present an analysis of their radial color gradients. We confirm that nearby elliptical and early- to mid-type spiral galaxies show either no or only small color gradients, becoming slightly bluer with radius. In contrast, we find that late-type spiral, irregular, peculiar, and merging galaxies become on average redder with increasing distance from the center. The scatter in radial color gradient trends increases toward later Hubble type. As a preliminary analysis of a larger data set obtained with the Hubble Space Telescope (HST), we also analyze the color gradients of six nearby galaxies observed with NICMOS in the near-IR (H) and with WFPC2 in the mid-UV (F300W) and red (F814W). We discuss the possible implications of these results on galaxy formation and compare our nearby galaxy color gradients to those at high redshift. We present examples of images and UBVR radial surface brightness and color profiles, as well as of the tables of measurements; the full atlas and tables are published in the electronic edition only.
We present the size evolution of passively evolving galaxies at z ~ 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to ...the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z > ~ 1.5. We identify 30 galaxies in ~40 arcmin super(2) to H < 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 mu m < ~ lambda sub(obs) < ~ 1.6 mu m with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of ~0.033(1 + z). We determine effective radii from Sersic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (Mlow * ~ 10 super(11) M) undergo the strongest evolution from z ~ 2 to the present. Parameterizing the size evolution as (1 + z) super(- alpha ), we find a tentative scaling of alpha approx = (- 0.6 + or - 0.7) + (0.9 + or - 0.4)log(Mlow */10 super(9) M sub(middot in circle)), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of high-redshift systems. We discuss the implications of this result for the redshift evolution of the Mlow *-R sub(e) relation for red galaxies.
The Radio/Optical Catalog of the SSA 13 Field Fomalont, E. B; Kellermann, K. I; Cowie, L. L ...
The Astrophysical journal. Supplement series,
12/2006, Letnik:
167, Številka:
2
Journal Article
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We present a 1.4 GHz catalog of 810 radio sources (560 sources in the complete sample) found in the SSA 13 field (R.A. = 13 super(h)12 super(m), decl. = 4238'). The 1.4 GHz radio image was obtained ...from a 91 hr VLA integration with an rms noise level of 4.82 kJy beam super(-1) at the field center. Optical images in the R band (6300 A) and z band (9200 A) with 3 s detection magnitudes of 26.1 and 24.9, respectively, were obtained from three observing nights on the 8 m Subaru Telescope. We find that 88% c 2% of the radio sources are identified with an optical counterpart. There is significantly more reddening for the optical counterparts that are fainter than 24 mag, probably caused by the somewhat larger redshifts of these faint galaxies. The radio and optical parameters are tabulated, and source morphologies are displayed by radio contours overlaid on optical false-color images. The brightness distributions show a wealth of complexity and are classified into a small number of categories. About one-third of the radio sources are larger than l."2, and their orientation is often similar to that of the associated galaxy or binary galaxy system. Radio emission is sometimes located outside of the nuclear regions of the galaxy. The density of sources in the SSA 13 field above 75 kJy is 0.40 arcmin super(-2), with a slope of -2.43 in the differential counts. This source density is somewhat higher than that in the Hubble Deep Field North. The radio spectral index may steepen for sources below 75 kJy and is consistent with the difference in the slope of the source counts observed between 1.4 and 8.4 GHz. We estimate that at most 40% of the microjansky radio sources are dominated by AGN processes, while the remainder are mostly the consequence of star formation and associated supernova activity.
Context. The reionization of the Universe is one of the most important topics of present-day astrophysical research. The most plausible candidates for the reionization process are star-forming ...galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the H I ionizing background at z greater than or similar to 3. Aims. We measure the Lyman continuum escape fraction, which is one of the key parameters used to compute the contribution of star-forming galaxies to the UV background. It provides the ratio between the photons produced at lambda <= 912 angstrom rest-frame and those that are able to reach the inter-galactic medium, i.e. that are not absorbed by the neutral hydrogen or by the dust of the galaxy's inter-stellar medium. Methods. We used ultra-deep U-band imaging (U = 30.2 mag at 1 sigma) from Large Binocular Camera at the Large Binocular Telescope (LBC/LBT) in the CANDELS/GOODS-North field and deep imaging in the COSMOS and EGS fields in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27 <= z <= 3.40 to faint magnitude limits (L = 0.2L*, or equivalently M-1500 similar to -19). The narrow redshift range implies that the LBC U-band filter exclusively samples the lambda <= 912 angstrom rest-frame wavelengths. Results. We measured through stacks a stringent upper limit (<1.7% at 1 sigma) for the relative escape fraction of H I ionizing photons from bright galaxies (L > L*), while for the faint population (L = 0.2L*) the limit to the escape fraction is less than or similar to 10%. We computed the contribution of star-forming galaxies to the observed UV background at z similar to 3 and find that it is not sufficient to keep the Universe ionized at these redshifts unless their escape fraction increases significantly (>= 10%) at low luminosities (M-1500 >= -19). Conclusions. We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature, and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental in order to measure the Lyman continuum escape fraction down to faint magnitudes (M-1500 similar to -16) that are inaccessible with the present instrumentation on blank fields. These results will be important in order to quantify the role of faint galaxies to the reionization budget.
We report on deep near-infrared F125W (J) and F160W (H) Hubble Space Telescope Wide Field Camera 3 images of the z = 6.42 quasar J1148+5251 to attempt to detect rest-frame near-ultraviolet emission ...from the host galaxy. These observations included contemporaneous observations of a nearby star of similar near-infrared colors to measure temporal variations in the telescope and instrument point-spread function (PSF). We subtract the quasar point source using both this direct PSF and a model PSF. Using direct subtraction, we measure an upper limit for the quasar host galaxy of m sub(J) > 22.8 and m sub(H) > 23.0 AB mag (2sigma). After subtracting our best model PSF, we measure a limiting surface brightness from 0".3 to 0".5 radius of mu sub(J) > 23.5 and mu sub(H) > 23.7 AB mag arcsec super(-2) (2sigma). We test the ability of the model subtraction method to recover the host galaxy flux by simulating host galaxies with varying integrated magnitude, effective radius, and Sersic index, and conducting the same analysis. These models indicate that the surface brightness limit ( mu sub(J) > 23.5 AB mag arcsec super(-2)) corresponds to an integrated upper limit of m sub(J) > 22-23 AB mag, consistent with the direct subtraction method. Combined with existing far-infrared observations, this gives an infrared excess log(IRX) > 1.0 and corresponding ultraviolet spectral slope beta > -1.2 + or - 0.2. These values match those of most local luminous infrared galaxies, but are redder than those of almost all local star-forming galaxies and z Asymptotically = to 6 Lyman break galaxies.
We investigate the evolution of the faint-end slope of the luminosity function, alpha , using semianalytical modeling of galaxy formation. In agreement with observations, we find that the slope can ...be fitted well by alpha (z) = alpha + bz, with alpha = -1.13 and b = -0.1. The main driver for the evolution in a is the evolution in the underlying dark matter mass function. Sub-L unk galaxies reside in dark matter halos that occupy a different part of the mass function. This part of the mass function is steeper at high redshifts than at low redshifts, and hence a is steeper. Supernova feedback in general causes the same relative flattening with respect to the dark matter mass function. The faint-end slope at low redshifts is dominated by field galaxies, and at high redshifts by cluster galaxies. The evolution of alpha (z) in each of these environments is different, with field galaxies having a slope b = -0.14 and cluster galaxies having a slope b = -0.05. The transition from a cluster-dominated to a field-dominated faint-end slope occurs roughly at a redshift z. unk 2 and suggests that a single linear fit to the overall evolution of alpha (z) might not be appropriate. Furthermore, this result indicates that tidal disruption of dwarf galaxies in clusters cannot play a significant role in explaining the evolution of alpha (z) at z < z. In addition, we find that different star formation efficiencies alpha . in the Schmidt-Kennicutt law and supernova-feedback efficiencies e generally do not strongly influence the evolution of alpha (z).
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