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Full-Text Articles in Physical Sciences and Mathematics
The Morphology Of Nine Radio-Selected Faint Galaxies From Deep Hubble Space Telescope Imaging, Nathan D. Roche, James D. Lowenthal, David C. Koo
The Morphology Of Nine Radio-Selected Faint Galaxies From Deep Hubble Space Telescope Imaging, Nathan D. Roche, James D. Lowenthal, David C. Koo
Astronomy: Faculty Publications
Using the Hubble Space Telescope (HST) WFPC2 we perform deep I-band imaging of nine radio-selected [F(8.5 GHz) ≥ 14 μJy] faint galaxies from the Roche, Lowenthal & Koo (2002) sample. Two are also observed in V using HST STIS. Six of the galaxies have known redshifts, in the range 0.4 < z < 1.0. Radial intensity profiles indicate that seven are disc galaxies and two are bulge-dominated. Four of the six with redshifts have a high optical surface brightness in comparison with previous studies of disc galaxies at similar redshifts (e.g. Lilly et al. 1998). The HST imaging reveals that two of the nine galaxies are in close interacting pairs and another five show morphological evidence of recent interactions - two are very asymmetric (A ∼ 0.4) and three have large, luminous rings resembling the collisional starburst rings in the Cartwheel galaxy. For the two ring galaxies with redshifts, we measure ring radii of 7.05 and 10.0 h kpc, which suggest post-collision ages 0.1-0.2 Gyr. One has a fainter inner ring, like the original Cartwheel. The remaining two appear to be late-type barred galaxies and relatively undisturbed. Our HST imaging confirms the high incidence of interactions and dynamical disturbance in faint radio-selected galaxies, as reported by Windhorst et al. and Serjeant et al., for example. In the great majority of these galaxies the high radio luminosities are probably the result of interaction-triggered starbursts. However, one interacting galaxy is a very radio-luminous giant elliptical, with red V - I colours, a normal surface brightness and no evidence of star-forming regions, so its radio source is probably an obscured active galactic nucleus (AGN). The mixture of observed morphologies suggests that enhanced radio luminosities often persist to a late stage of interaction, i.e. at least ∼0.2 Gyr after the perigalactic encounter. asym 50 -1
Keck Spectroscopy And Imaging Of Faint Galaxies Identified As Microjansky Radio Sources, Nathan D. Roche, James D. Lowenthal, David C. Koo
Keck Spectroscopy And Imaging Of Faint Galaxies Identified As Microjansky Radio Sources, Nathan D. Roche, James D. Lowenthal, David C. Koo
Astronomy: Faculty Publications
We investigate the nature of the faintest radio sources detected in three Very Large Array surveys, to F(8.5 GHz) ∼ 8 μJy. Using the Keck low-resolution imaging spectrograph in BRI and the near-infrared camera in K′ (2.1 μm), we image 51 radio sources, and identify probable optical counterparts for 50. With low-resolution imaging spectroscopy, we successfully acquire new redshifts for 17 sources. Combining these with nine prior redshifts, we can then analyse a sample of 26 sources with spectroscopic redshifts. Based on this sample of 26, we find the largest contribution, about 60 per cent (15), to be from disc …