arXiv subjects

Arjun Dey

Publications and source records attributed to Arjun Dey.

328 records · Page 19Linked to original sources

arXiv1995

What is 3C 324?

We report ground based and HST observations of the z=1.206 radio galaxy 3C 324, a prototypical example of the radio-optical ``alignment effect.'' While infrared images shows a simple, round object reminiscent of a giant elliptical galaxy, the HST images reveal a spectacular, linear chain of UV-bright subcomponents closely aligned with the radio axis. In light of the available data, we consider various scenarios to explain the properties of 3C 324, as well as evidence for the presence of dust which may obscure the central active nucleus and scatter its light to produce the polarized, aligned continuum seen in the rest-frame UV.

astro-ph↗

arXiv1995

The Radio Galaxy 3C265 Contains a Hidden Quasar Nucleus

We report the discovery of broad MgII emission from the high redshift radio galaxy 3C265 (z=0.81). We detect the broad line in the nuclear spectrum and in the spatially extended galaxian component, both near the nucleus and in the spectrum of an off-nuclear knot located 31 kpc south east of the nucleus of the galaxy. These data provide strong support for the simplest form of the unification hypothesis, that radio galaxies are quasars whose optical radiation is directed in the plane of the sky rather than into our line of sight. These data also strongly support the scattering model for the alignment of the UV continuum emission with the radio axis. In 3C265, if the axis of the anisotropically emitted UV continuum radiation is identified with the major axis of the radio source, then the observed rest frame UV continuum emission implies that the opening angle of the radiation cone is large (half angle approximately 45 degrees). We also derive a mass estimate of 8x10^{10} Msun for the central region of 3C265 from its rotation curve. The implied mass-to-light ratio is low (M/L is roughly 2), and suggests that a significant fraction of the rest frame UV continuum emission from this galaxy is dominated by reprocessed radiation from the buried AGN. Finally, we detect the CaII\lambda3933 K line in absorption in the integrated spectrum of 3C265. This provides direct spectroscopic evidence for the existence of stars in a high redshift radio galaxy.

astro-ph↗

arXiv1994

Discovery of a z=2.76 Dusty Radio Galaxy?

We report the discovery of a z=2.76 radio galaxy, MG1019+0535, with an unusual spectrum. Ly$α$, which usually dominates the spectra of high redshift radio galaxies, is very weak and the strongest lines in the spectrum are CIV$λ$1549 and HeII$λ$1640. We speculate that dust is responsible for attenuating the Ly$α$ line. This object provides more evidence for dust formation at early epochs. The optical counterpart of the compact radio source has a double morphology which is orthogonal to the radio source axis and most likely due to the superposition of two distinct objects which may or may not be physically related. There is only one detected line from the brighter component (B) which is close in observed wavelength to the redshifted HeII$λ$1640 line from the z=2.76 galaxy (A). We discuss whether B is at the same redshift as A or whether it is a foreground galaxy at z=0.66. We also report the serendipitous discovery of a very red ($R-K>7$) field object.

astro-ph↗

arXiv1994

Keck Observations of the Most Distant Galaxy: 8C1435+63 at z=4.25

We report on Keck observations and confirm the redshift of the most distant galaxy known: 8C1435+63 at z=4.25. The spectrum shows a strong Ly$α$ line, a Ly$α$ forest continuum break and a continuum break at $λ_{rest}=912$Å. The Ly$α$ emission is spatially extended and roughly aligned with the radio source. The galaxy shows a double structure in the $I$-band ($λ_{rest}\approx$1500Å) which is aligned with the radio axis; the two $I$-band components spatially coincide with the nuclear and southern radio components. Some fraction of the $I$ band emission could be due to a nonthermal process such as inverse compton scattering. In the $K$-band ($λ_{rest}\approx$4200Å), which may be dominated by starlight, the galaxy has a very low surface brightness, diffuse morphology. The $K$ morphology shows little relationship to the radio source structure, although the major axis of the $K$ emission is elongated roughly in the direction of the radio source axis. The galaxian continuum is very red ($I-K>4$) and if the $K$ continuum is due to starlight, implies a formation redshift of $z_f > 5$. We speculate that this galaxy may be the progenitor of a present day cD galaxy.

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