arXiv subjects

J. E. Larkin

Publications and source records attributed to J. E. Larkin.

24 records · Page 2Linked to original sources

arXiv2000

K-Band Spectroscopy of an Obscured Massive Stellar Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC

We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039) with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the vicinity of the southern nucleus (NGC 4039) in 0.39" seeing in K-band using NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the highest surface brightness peak in the mid-IR (12-18 um) ISO image presented by Mirabel et al (1998). We obtained high signal-to-noise 2.03-2.45 um spectra of the nucleus and the obscured star cluster at R = 1900. The cluster is very young (age ~ 4 Myr), massive (M ~ 16E6 M_sun), and compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius), assuming a Salpeter IMF (0.1-100 M_sun). Its hot stars have a radiation field characterized by T_eff ~ 39,000 K, and they ionize a compact HII region with n_e ~ 10^4 cm^(-3). The stars are deeply embedded in gas and dust (A_V = 9-10 mag), and their strong FUV field powers a clumpy photodissociation region with densities n_H > 10^5 cm^(-3) on scales of ~ 200 pc, radiating L{H_2 1-0 S(1)}= 9600 L_sun.

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arXiv1999

Infrared Spectroscopy of a Massive Obscured Star Cluster in the Antennae Galaxies (NGC 4038/4039) with NIRSPEC

We present infrared spectroscopy of the Antennae Galaxies (NGC 4038/4039) with NIRSPEC at the W. M. Keck Observatory. We imaged the star clusters in the vicinity of the southern nucleus (NGC 4039) in 0.39" seeing in K-band using NIRSPEC's slit-viewing camera. The brightest star cluster revealed in the near-IR (M_K(0) = -17.9) is insignificant optically, but coincident with the highest surface brightness peak in the mid-IR (12-18 micron) ISO image presented by Mirabel et al. (1998). We obtained high signal-to-noise 2.03 - 2.45 micron spectra of the nucleus and the obscured star cluster at R ~ 1900. The cluster is very young (4 Myr old), massive (16e6 M_sun), and compact (density ~ 115 M_sun pc^(-3) within a 32 pc half-light radius), assuming a Salpeter IMF (0.1 - 100 M_sun). Its hot stars have a radiation field characterized by T_eff ~ 39,000 K, and they ionize a compact H II region with n_e ~ 1e4 cm^(-3). The stars are deeply embedded in gas and dust (A_V ~ 9-10 mag), and their strong FUV field powers a clumpy photodissociation region with densities n_H >= 1e5 cm^(-3) on scales of up to 200 pc, radiating L[H_2 1-0 S(1)] = 9600 L_sun.

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arXiv1999

Faint Field Galaxies Around Bright Stars - A New Strategy for Imaging at the Diffraction Limit

This paper presents a new strategy for observing faint galaxies with high order natural guide star systems. We have imaged 5 high galactic latitude fields within the isoplanatic patch of bright stars (8.5 < R < 10.3 mag). The fields provide a rich set of faint field galaxies that are observable with a natural guide star adaptive optics system on a large telescope. Due to the small fields of many AO science cameras, these preliminary images are necessary to identify candidate galaxies. We present the photometry and positions for 78 objects (at least 40 galaxies) near five bright stars, appropriate for diffraction limited studies with the Keck and other AO systems on large ground-based telescopes. The K band seeing conditions in each field were excellent (0.4" - 0.7") allowing us to identify stars and estimate galaxy sizes. We also simulate AO images of field galaxies to determine the feasibility of infrared morphological studies at the diffraction limit. With new high order AO systems coming on line with 8-10 meter class telescopes, we believe these observations are invaluable in beginning to study faint galaxy populations at the diffraction limit.

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arXiv1999

Infrared Spectroscopy of the High Redshift Radio Galaxy MRC~2025-218 and a Neighboring Extremely Red Galaxy

This paper presents infrared spectra taken with the newly commissioned NIRSPEC spectrograph on the Keck Telescope of the High Redshift Radio Galaxy MRC 2025-218 (z=2.630) and an extremely red galaxy (R-K > 6 mag) 9'' away. These observations represent the deepest infrared spectra of a radio galaxy to date and have allowed for the detection of Hbeta, OIII (4959/5007), OI (6300), Halpha, NII (6548/6583) and SII (6716/6713). The Halpha emission is very broad (FWHM~6000 km/s) and strongly supports AGN unification models linking radio galaxies and quasars. The line ratios are most consistent with a partially obscured nuclear region and very high excitation. The OIII (5007) line is extended several arcseconds and shows high velocity clouds in the extended emission. The nucleus also appears spectrally double and we argue that the radio galaxy is undergoing a violent merger process. The red galaxy, by comparison, is very featureless even though we have a good continuum detection in the H and K bands. We suggest that this object is a foreground galaxy, probably at a redshift less than 1.5.

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arXiv1999

Image Slicing with Infrared Fibers

We are proposing to build a new integral field instrument (OSIRIS) for use with the Keck Adaptive Optics System. It will utilize a large (1024 element) fiber optic bundle to slice the field and feed a standard infrared spectrograph with a spectral resolution of 5000. To improve the fill factor of the fiber bundle, we plan on coupling it to a matched lenslet array. The spectrograph will have three plate scales of 0.05'', 0.10'' and 0.20'' per pixel, and full broad band spectra will fit on a single 2048x2048 infrared array. Other innovations include using some of the fibers for pseudo-slits and sky measurements and non-uniform spacing for the "linear" feed to the spectrograph.

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arXiv1997

A Near Infrared Spectroscopic Survey of LINER Galaxies

This paper reports the results of a near infrared spectroscopic survey of LINER galaxies undertaken with a new infrared spectrograph at the 5 m Hale telescope. The galaxy sample includes 11 LINERs with spectra covering the [FeII] (1.2567 microns), PaBeta (1.2818 microns), H2 (1-0 S(1), 2.1218 microns) and BrGamma (2.1655 microns) near infrared emission lines, and one additional galaxy with only [FeII] and Pa$β$ line coverage. All of the LINERs with infrared line detections have strong [FeII] and/or H2 emission, with about half (4 out of 9) having extremely high ratios (>2) of [FeII] to PaBeta. The strength of the H2 and [FeII] lines is well correlated with the optical [OI] line, with many LINERs having higher ratios of [FeII]/PaBeta, H2/BrGamma and [OI]/H-Alpha than other galaxy types. The LINERs with the highest [FeII]/PaBeta ratios (termed ``strong'' [FeII] LINERs) show evidence for recent star formation. Shocks from compact supernova remnants may enhance the [FeII] emission in these ``strong'' [FeII] LINERs. The LINERs with lower [FeII]/PaBeta ratios (termed ``weak'' [FeII] LINERs) are more consistent with Seyfert-like activity, including higher ionization states, some strong x-ray sources and some broad H-Alpha detections. The [FeII] luminosity and the [FeII]/PaBeta ratio in these objects are more easily explained by hard x-ray excitation than in the ``strong'' [FeII] LINERs. These ``weak'' [FeII] LINERs are considered prime candidates for being low luminosity Seyfert nuclei.

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