arXiv subjects

James R. Graham

Publications and source records attributed to James R. Graham.

151 records · Page 9Linked to original sources

arXiv1996

Colors and K-Band Counts of Extremely Faint Field Galaxies

We combine deep K-band (Keck) with V- and I-band (NTT) observations of two high-Galactic latitude fields, surveying a total of ~2 sq. arcmin. The K-band galaxy counts continue to rise above K=22, reaching surface densities of few x 10^5 per sq. degree. The slope for the counts is (d log(N) per mag per sq. degree) = 0.23 +/- 0.02 between K=18-23, consistent with other deep K surveys. The numbers of galaxies in each mag bin is about two times greater than the galaxy counts of Djorgovski et al. (1995). The optical and near infrared magnitudes of all objects detected in the V+I+K image are discussed in the context of grids of isochrone synthesis galaxy evolutionary models (Bruzual & Charlot 1993, 1995). The colors of most of the observed galaxies are consistent with a population drawn from a broad redshift distribution. A few galaxies at K=19-20 are red in both colors (V-I>3; I-K>2), consistent with being early-type galaxies having undergone a burst of star formation at z>5 and viewed at z~1. At K>20, we find ~8 ``red outlier'' galaxies with I-K>4 and V-I<2.5, whose colors are difficult to mimic by a single evolving or non-evolving stellar population at any redshift. They are likely either low-metallicity, dusty dwarf galaxies, or old galaxies at high redshift (z>1.2). Their surface density is several per square arcminute, which is so high that they are probably common objects of low luminosity $L<L_*$.

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arXiv1996

IRAS FSC 15307+3252 -- Gravitationally Lensed Seyfert or Cannibal Elliptical at $z$ = 0.93?

We present the highest spatial and spectral resolution near-infrared data to date of the $\sim~10^{13}~h^{-2}~L_{\sun}$ {\sl IRAS} source FSC 15307+3252 at $z = 0.93$, apparently the most luminous galaxy in the known Universe. Deep $K$-band (2.2 \micron) images taken in 0\farcs4 seeing at the W.\ M.\ Keck Telescope reveal three components within 2\arcsec. The dominant component has a surface brightness profile well-characterized by an $r^{1/4}$ law and a nucleus which is stellar in appearance with extended structure, possibly a second nucleus $\sim$~0\farcs5 away. Our 1.1--1.4~\micron\ spectrum shows strong emission lines of \oi\ \lam\lam6300, 6364; blended \ha~+~\nii\ \lam\lam6548, 6583; and \sii\ \lam\lam6716, 6731 with characteristics of Seyfert 2 galaxies. The \ha\ line also has a broad (1900 km~s$^{-1}$) component. In light of the recent discovery that FSC 10214+4724, previously the most luminous known galaxy, is a gravitationally-lensed system, we explore the possibility that F15307 is also lensed. Quantitative arguments are inconclusive, but aspects of F15307's morphology do suggest lensing; the system bears a strong resemblance to quadruple-image gravitational lenses. On the other hand, given the $r^{1/4}$ profile, the close companions, and the active nucleus, F15307 may in fact be a giant elliptical galaxy caught in the act of galactic cannibalism, a scenario which could also account for its unparalleled luminosity.

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arXiv1996

The Spectroscopic Redshift of an Extremely Red Object and the Nature of the Very Red Galaxy Population

Infrared surveys have discovered a significant population of bright (K<19) extremely red (R-K>6) objects. Little is known about the properties of these objects on account of their optical faintness (R>24). Here, we report deep infrared imaging and spectroscopy of one of the extremely red objects (EROs) discovered by Hu \& Ridgway (1994) in the field of the z=3.79 quasar PC1643+4631A. The infrared images were obtained in 0.5" seeing, and show that the object (denoted HR10) is not a dynamically relaxed elliptical galaxy dominated by an old stellar population as was previously suspected, but instead has an asymmetric morphology suggestive of either a disk or an interacting system. The infrared spectrum of HR10 shows a single, possibly broad emission feature at 1.60um which we identify as Halpha+[NII] at z=1.44. The luminosity and width of this emission line indicates either intense star formation (about 20h^{-2} solar masses/yr) or the presence of an active nucleus. Based on the rest frame UV-optical spectral energy distribution, the luminosity of HR10 is estimated to be 3 to 8 L*. The colors of HR10 are unusually red for a galaxy (at z=1.44 the age of HR10 is at most 2 to 8 Gyr depending on cosmology), and indicate that HR10 is dusty. HR10 is detected weakly at radio wavelengths; this is consistent with either the starburst or AGN hypothesis. If HR10 is a typical representative of its class, EROs are numerous and represent a significant component of the luminous objects in the Universe at z approx 1.5.

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arXiv1995

Tracing the Dynamics of Disk Galaxies with Optical and IR Surface Photometry: Color Gradients in M99

We present optical and IR surface photometry of M99 (NGC 4254) at g, r_S i, J and K'. We also present a K' image of M51 (NGC 5194) for comparison. Fourier decomposition of the disk light reveals that the radial distribution of power depends on wavelength, which in turn implies that the spiral structure traced in the visual (i.e. young population I and dust) is different from the one detected at 2 microns (i.e. old stellar disk). We observe radial modulation of the power and a dependency of power with wavelength that are consistent with modal theory of spiral structure. A central motivation for our research is the fundamental idea of density wave theory that the passage of a spiral density wave triggers star formation. We have found a stellar population age gradient consistent with this scenario in a reddening-free, red supergiant-sensitive, Q-like photometric parameter at 6 kpc galactocentric distance across one of the arms of M99. We rule out that the change in this parameter, Q(r_SJgi), across the arm is mainly due to dust. The difference in Q(r_SJgi) going from the interarm regions to the arms also indicates that arms cannot be due exclusively to crowding of stellar orbits. We present the first measurement of Omega_p, the angular speed of the spiral pattern, and of the location of the corotation radius, derived from the drift velocity of the young stars away from their birth site. The measured Q(r_SJgi) implies a star formation rate for M99 within the range of 10-20 M_odot/yr; a disk stellar mass surface density of ~80 M_odot/pc^2; and a maximum contribution of ~20 percent from red supergiants to the K' light in a small region, and much smaller on average. We measure a K' arm--interarm contrast of 2-3, too high for M99 to be a truly isolated galaxy.

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arXiv1995

Mid-Infrared Imaging of Young Stellar Objects

We present arcsecond resolution mid-infrared (8--13 $μ$m) images and photometry of four young stellar objects (YSOs)~--- L1551-IRS5, HL~Tau, AS~205, and AS~209 (V1121~Oph)~--- taken with the Berkeley Mid-Infrared Camera. For AS~205, a known T Tauri binary, we also present near-infrared JHK images and HKL$^{\prime}$ speckle imaging data. All three single stars are unresolved in our mid-IR images. Our data is the first to resolve in the mid-IR both components of the close binary AS~205 (projected separation $\sim$1.3$^{\prime \prime}$ (210~A.U.)). AS~205~North is the IR brighter star in our data while published observations find it to be the optically fainter star. Pre-main sequence evolutionary models suggest the AS~205 system is non-coeval; we discuss possible explanations for this result and comment on the circumstellar material and evolutionary status of this young binary. Nearly all of our objects exhibit changes in their mid-IR flux in measurements separated by intervals of days up to many years; the variations range from 30--300\%. We speculate that the cause of the variability lies in the accretion disks of these objects; the data suggest disk accretion rate fluctuations of nearly an order of magnitude. The existence of large mid-IR variability argues that simultaneous multiwavelength observations are needed for a proper analysis of YSO spectral energy distributions.

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arXiv1995

High Resolution Infrared Imaging of FSC10214+4724: Evidence for Gravitational Lensing

We present near--infrared observations of the ultraluminous high-redshift (z=2.286) IRAS source FSC 10214+4724 obtained in 0.''4 seeing at the W. M. Keck telescope. These observations show that FSC 10214+4724 consists of a highly symmetric circular arc centered on a second weaker source. The arc has an angular extent of about 140 degrees and is probably unresolved in the transverse direction. This morphology constitutes compelling prima facie evidence for a gravitationally lensed system. Our images also contain evidence for the faint counter image predicted by the lens hypothesis. The morphology of FSC 10214+4724 can be explained in terms of a gravitationally lensed background source if the object at the center of curvature of the arc is an L* galaxy at z ~ 0.4. If FSC 10214+4724 is lensed then there is significant magnification and its luminosity has been overestimated by a large factor. Our results suggest FSC~10214+4724 is not a uniquely luminous object but ranks amo ng the most powerful quasars and ultraluminous IRAS galaxies.

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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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