arXiv subjects

P. N. Appleton

Publications and source records attributed to P. N. Appleton.

At least 91 records · Page 5Linked to original sources

arXiv2004

Fire and Ice: IRS Mid-IR Spectroscopy of IRAS F00183--7111

We report the detection of strong absorption and weak emission features in the 4--27 micron Spitzer-IRS spectrum of the distant ultraluminous infrared galaxy (ULIRG) IRAS F00183--7111 (z=0.327). The absorption features of CO2 and CO gas, water ice, hydrocarbons and silicates are indicative of a strongly obscured (A[9.6]>=5.4; A[V]>=90) and complex line of sight through both hot diffuse ISM and shielded cold molecular clouds towards the nuclear power source. From the profile of the 4.67 micron CO fundamental vibration mode we deduce that the absorbing gas is dense (n~10^6 cm^-3) and warm (720 K) and has a CO column density of ~10^19.5 cm^-2, equivalent to N[H]~10^23.5 cm^-2. The high temperature and density, as well as the small infered size (<0.03pc), locates this absorbing gas close to the power source of this region. Weak emission features of molecular hydrogen, PAHs and Ne+, likely associated with star formation, are detected against the 9.7 micron silicate feature, indicating an origin away from the absorbing region. Based on the 11.2 micron PAH flux, we estimate the star formation component to be responsible for up to 30% of the IR luminosity of the system. While our mid-infrared spectrum shows no tell-tale signs of AGN activity, the similarities to the mid-infrared spectra of deeply obscured sources (e.g. NGC4418) and AGN hot dust (e.g. NGC1068), as well as evidence from other wavelength regions, suggest that the power source hiding behind the optically thick dust screen may well be a buried AGN.

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arXiv2004

Rest-Frame MIR Detection of an Extremely Luminous Lyman Break Galaxy with the Spitzer IRS

We present the first rest-frame ~4 micron detection of a Lyman break galaxy. The data were obtained using the 16 micron imaging capability of the Spitzer Infrared Spectrograph. The target object, J134026.44+634433.2, is an extremely luminous Lyman break galaxy at z=2.79 first identified in Sloan Digital Sky Survey spectra (Bentz, Osmer, & Weinberg 2004). The source is strongly detected with a flux of 0.94 +/- 0.02 mJy. Combining Spitzer and SDSS photometry with supporting ground-based J- and K-band data, we show that the spectral energy distribution is consistent with an actively star-forming galaxy. We also detect other objects in the Spitzer field of view, including a very red MIR source. We find no evidence of a strong lens amongst the MIR sources.

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arXiv2004

Imaging of High Redshift Submillimeter Galaxies at 16 and 22microns with the Spitzer/IRS: Revealing a population at z>2.5

We present broad band imaging observations obtained with the ``peak up'' imagers of the Spitzer Space Telescope Infrared Spectrograph (IRS) at wavelengths of 16micron and 22micron for a number of sources detected primarily at submillimeter wavelengths, which are believed to be at high, though undetermined, redshift. We targeted 11 sources originally detected by SCUBA and 5 submillimeter sources detected at 1.2mm by MAMBO. Two optically discovered quasars with z>6 were also observed to determine if there is detectable dust emission at such high redshifts. Seven of the submillimeter sources and both high-redshift quasars were detected, and upper limits of about ~50microJy apply to the remainder. Using their mid-/far-IR colors, we demonstrate that all of the submillimeter sources are at z>1.4. The mid-IR colors for two of our detections and three of our strong upper limits suggest that these galaxies must be at z>2.5. We also introduce a technique for estimating redshifts and source characteristics based only on the ratio of fluxes in the 16micron and 22micron images.

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arXiv2004

MARCS-Model Stellar Atmospheres, and Their Application to the Photometric Calibration of the Spitzer-IRS

We describe state-of-the-art MARCS-code model atmospheres generated for a group of A dwarf, G dwarf, and late-G to mid-K giant standard stars, selected to photometrically calibrate the Spitzer-IRS, and compare the synthetic spectra to observations of HR 6688, HR 6705, and HR 7891. The general calibration processes and uncertainties are briefly described, and the differences between various templated composite spectra of the standards are addressed. In particular, a contrast between up-to-date model atmospheres and previously published composite and synthetic spectra is illustrated for wavelength ranges around 8um (where the SiO Delta(v) = 1 band occurs for the cooler standards) and lambda greater than 20um, where the use of the Engelke function will lead to increasingly large discrepancies due to the neglect of gravity in cool stars. At this point, radiometric requirements are being met, absolute flux calibration uncertainties (1-sigma) are ~20% in the SH and LH, and ~15% in the SL and LL data, and order-to-order flux uncertainties are ~10% or less. Iteration between the MARCS model atmosphere inputs and the data processing will improve the S/N ratios and calibration accuracies.

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arXiv2004

Spatially Resolved Ultraviolet, H-alpha, Infrared, and Radio Star Formation in M81

We present Multiband Imaging Photometer for Spitzer (MIPS) observations of M81 at 24, 70, and 160 micron. The grand design nature of M81 is clearly seen, showing two well resolved spiral arms containing numerous bright star forming regions. The MIPS images reveal a significant amount of cold dust associated with the spiral arms. We investigate the variation of the ultraviolet (UV), H-alpha, and infrared (IR) luminosities and star formation rate (SFR) indicators across the face of M81 using the MIPS images and archival UV and H-alpha images. For regions in M81, we find that UV and H-alpha SFRs (uncorrected for dust attenuation) are always lower than the IR SFR. The cause of this behavior is dust attenuation and/or using SFR calibrations appropriate for entire galaxies, not regions in galaxies. The characteristics of the dust attenuation for the regions indicate the dust grains and/or geometry are different from those in starburst galaxies. The behavior of the infrared-radio correlation in M81 is seen to vary from the global average, with variations correlated with the morphology of M81.

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arXiv2004

The Far- and Mid-Infrared/Radio Correlations in the Spitzer Extragalactic First Look Survey

Using the SPITZER SPACE TELESCOPE and the VLA, we present the first DIRECT evidence that the well-known far-infrared/radio correlation is valid to cosmologically significant redshift. We also confirm, with improved statistics compared with previous surveys, a similar result for the Mid-IR/radio correlation. We explore the dependence of monochromatic q_{24} and q_{70} on z. The results were obtained by matching Spitzer sources at 24 and 70 microns with VLA 1.4 GHz micro-Jy radio sources obtained for the SPITZER FLS. Spectroscopic redshifts have been obtained for over 500 matched IR/radio sources using observations at WIYN, Keck and archival SDSS data extending out to z > 2. We find that q_{24} shows significantly more dispersion than q_{70}. By comparing the observed fluxes at 70, 24 and 4.5 microns with a library of SED templates, we find that the larger dispersion in q_{24} is predictable in terms of systematic variations in SED shape throughout the population. Although the models are not able to encompass the full range of observed behavior (both the presence of either extremely flat or extremely steep IR SEDs), the fitting parameters were used to `k-correct' the higher-z galaxies which resulted in a reduced scatter in q. For comparison, we also corrected these data using the SED for M82. The results for 24 and 70 microns provide strong consistent evidence for the universality of the mid-IR/radio and far-IR/radio correlations out to redshifts of at least z = 1.

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arXiv2004

Spitzer 24micron Observations of Optical/Near-IR Selected Extremely Red Galaxies: Evidence for Assembly of Massive Galaxies at z~1-2 ?

We carried out the direct measurement of the fraction of dusty sources in a sample of extremely red galaxies with (R - Ks) > 5.3mag and Ks < 20.2mag, using 24um data from the Spitzer Space Telescope. Combining deep 24um, Ks- and R-band data over an area of 64sq.arcmin in ELAIS N1, we find that 50%+-6% of our ERO sample have measurable 24um flux above the 3sigma flux limit of 40uJy. This flux limit corresponds to a SFR of 12Msun/yr at z~1. The 24um-detected EROs have 24-to-2.2 and 24-to-0.7um flux ratios consistent with infrared luminous, dusty sources at z>1, and an order of magnitude too red to be explained by an infrared quiescent spiral or a pure old stellar population at any redshift. Keck optical spectroscopy of a sample of similarly selected EROs in the FLS field suggests that most of the EROs in ELAIS N1 are probably at z~1. The mean 24um flux (167uJy) of the 24um-detected ERO sample roughly corresponds to the total infrared luminosity of (3-10)x10^(11)Lsun at z=1-1.5, which is similar to that of local LIRGs and ULIGs. The corresponding SFR is ~(50-170)Msun/yr. If the time scale of this starbursting phase is on the order of 10^8yr as inferred for the local LIRGs and ULIGs, the lower limit on the masses of these 24um-detected EROs is (5-20)x10^9Msun. It is plausible that some of the starburst EROs are in the midst of violent transformation to become massive early type galaxies at the epoch of z ~ 1-2.

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arXiv2004

Extragalactic Source Counts at 24 Microns in the Spitzer First Look Survey

We present the Spitzer MIPS 24 micron source counts in the Extragalactic First Look Survey main, verification and ELAIS-N1 fields. Spitzer's increased sensitivity and efficiency in large areal coverage over previous infrared telescopes, coupled with the enhanced sensitivity of the 24 micron band to sources at intermediate redshift, dramatically improve the quality and statistics of number counts in the mid-infrared. The First Look Survey observations cover areas of, respectively, 4.4, 0.26 and 0.015 sq.deg. and reach 3-sigma depths of 0.11, 0.08 and 0.03 mJy. The extragalactic counts derived for each survey agree remarkably well. The counts can be fitted by a super-Euclidean power law of index alpha=-2.9 from 0.2 to 0.9 mJy, with a flattening of the counts at fluxes fainter than 0.2 mJy. Comparison with infrared galaxy evolution models reveals a peak's displacement in the 24 micron counts. This is probably due to the detection of a new population of galaxies with redshift between 1 and 2, previously unseen in the 15 micron deep counts.

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arXiv2004

Characterization of Extragalactic 24micron Sources in the Spitzer First Look Survey

In this Letter, we present the initial characterization of extragalactic 24um sources in the Spitzer First Look Survey (FLS) by examining their counterparts at 8um and R-band. The color-color diagram of 24-to-8 vs. 24-to-0.7um is populated with 18,734 sources brighter than the 3sigma flux limit of 110uJy, over an area of 3.7sq.degrees. The 24-to-0.7um colors of these sources span almost 4 orders of magnitudes, while the 24-to-8um colors distribute at least over 2 orders of magnitudes. In addition to identifying ~30% of the total sample with infrared quiescent, mostly low redshift galaxies, we also found that: (1) 23% of the 24um sources (~1200/sq.degrees) have very red 24-to-8 and 24-to-0.7 colors and are probably infrared luminous starbursts with L(IR)>3x10^(11)Lsun at z>1. In particular, 13% of the sample (660/sq.degrees) are 24um detected only, with no detectable emission in either 8um or R-band. These sources are the candidates for being ULIRGs at z>2. (2) 2% of the sample (85/sq.degrees) have colors similar to dust reddened AGNs, like Mrk231 at z~0.6-3. (3) We anticipate that some of these sources with extremely red colors may be new types of sources, since they can not be modelled with any familiar type of spectral energy distribution. We find that 17% of the 24um sources have no detectable optical counterparts brighter than R limit of 25.5mag. Optical spectroscopy of these optical extremely faint 24um sources would be very difficult, and mid-infrared spectroscopy from the Spitzer would be critical for understanding their physical nature (Abridged).

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arXiv2004

Obscured and unobscured active galactic nuclei in the Spitzer Space Telescope First Look Survey

Selection of active galactic nuclei (AGN) in the infrared allows the discovery of AGN whose optical emission is extinguished by dust. In this paper, we use the Spitzer Space Telescope First Look Survey (FLS) to assess what fraction of AGN with mid-infrared luminosities comparable to quasars are missed in optical quasar surveys due to dust obscuration. We begin by using the Sloan Digital Sky Survey (SDSS) database to identify 54 quasars within the 4 deg^2 extragalactic FLS. These quasars occupy a distinct region in mid-infrared color space by virtue of their strong, red, continua. This has allowed us to define a mid-infrared color criterion for selecting AGN candidates. About 2000 FLS objects have colors consistent with them being AGN, but most are much fainter in the mid-infrared than the SDSS quasars, which typically have 8 micron flux densities, S(8.0), ~1 mJy. We have investigated the properties of the 43 objects with S(8.0) >= 1 mJy satisfying our AGN color selection. This sample should contain both unobscured quasars, and AGN which are absent from the SDSS survey due to extinction in the optical. After removing 16 known quasars, three probable normal quasars, and eight spurious or confused objects from the initial sample of 43, we are left with 16 objects which are likely to be obscured quasars or luminous Seyfert-2 galaxies. This suggests the numbers of obscured and unobscured AGN are similar in samples selected in the mid-infrared at S(8.0)~1 mJy.

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arXiv2003

Non-Nuclear Hyper/Ultraluminous X-Ray Sources in the Starbursting Cartwheel Ring Galaxy

We report the Chandra/ACIS-S detection of more than 20 ultraluminous X-ray sources (ULXs, L_{0.5-10 keV} >~ 3 x 10^{39} ergs/sec) in the Cartwheel collisional ring galaxy system, of which over a dozen are located in the outer active star-forming ring. A remarkable hyperluminous X-ray source (HLX, L_{0.5-10 keV} >~ 10^{41} ergs/sec assuming isotropic radiation), which dominates the X-ray emission from the Cartwheel ring, is located in the same segment of the ring as most ULXs. These powerful H/ULXs appear to be coincident with giant HII region complexes, young star clusters, and radio and mid-infrared hot-spots: all strong indicators of recent massive star formation. The X-ray spectra show that H/ULXs have similar properties as those of the {\it most luminous} ULXs found in the nearest starbursts and galaxy mergers such as the Antennae galaxies and M82. The close association between the X-ray sources and the starbursting ring strongly suggests that the H/ULXs are intimately associated with the production and rapid evolution of short-lived massive stars. The observations represent the most extreme X-ray luminosities discovered to date associated with star-forming regions--rivaling the X-ray luminosities usually associated with active galactic nuclei.

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arXiv2002

Azimuthal and Kinematic Segregation of Neutral and Molecular Gas in Arp 118: The Yin-Yang Galaxy NGC 1144

We present new high-resolution HI observations of the disk of the collisional infrared luminous (L$_{\rm IR}=2.2\times10^{11}$ L$_{\sun}$) galaxy NGC 1144, which reveal an apparent large-scale azimuthal and kinematic segregation of neutral hydrogen relative to the molecular gas distribution. Even among violently collisional galaxies, the CO/HI asymmetry in NGC 1144 is unusual, both in the inner regions, and in the outer disk. We suggest that we are observing Arp 118 at a special moment, shortly after a high-speed collision between NGC 1144 and its elliptical companion NGC 1143. HI emission with an average molecular fraction f$_{mol}$ $<$ 0.5 is observed on one side (NW) of the rotating disk of NGC 1144, while the other side (SE) is dominated by dense molecular complexes in which f$_{mol}$ is almost unity. The interface region between the warm-- and cool--cloud dominated regions, lies on a deep spiral-like dust-lane which we identify as a shock-wave responsible for the relative shift in the dominance of HI and H$_2$ gas. A strong shock being fed by diffuse HI clouds with unusually large ($>$ 400 km s$^{-1}$) rotational velocities can explain: 1) the CO/HI asymmetries, 2) a large velocity jump (185 km s$^{-1}$) across the arm as measured by HI absorption against a radio bright continuum source which straddles the arm, and 3) the asymmetric distribution of star formation and off-nuclear molecular gas resulting from likely streaming motions associated with the strong-shock. The new results provide for the first time a coherent picture of Arp 118's many peculiarities, and underlines the potentially complex changes in the gas-phase that can accompany large gravitational perturbations of gas-rich galaxies.

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arXiv2002

COLA II - Radio and Spectroscopic Diagnostics of Nuclear Activity in Galaxies

We present optical spectroscopic observations of 93 galaxies taken from the infra-red selected COLA (Compact Objects in Low Power AGN) sample. The sample spans the range of far-IR luminosities from normal galaxies to LIRGs. Of the galaxies observed, 78 (84%) exhibit emission lines. Using a theoretically-based optical emission-line scheme we classify 15% of the emission-line galaxies as Seyferts, 77% as starbursts, and the rest are either borderline AGN/starburst or show ambiguous characteristics. We find little evidence for an increase in the fraction of AGN in the sample as a function of far-IR luminosity but our sample covers only a small range in infrared luminosity and thus a weak trend may be masked. As a whole the Seyfert galaxies exhibit a small, but significant, radio excess on the radio-FIR correlation compared to the galaxies classified as starbursts. Compact (<0.05'') radio cores are detected in 55% of the Seyfert galaxies, and these galaxies exhibit a significantly larger radio excess than the Seyfert galaxies in which cores were not detected. Our results indicate that there may be two distinct populations of Seyferts, ``radio-excess'' Seyferts, which exhibit extended radio structures and compact radio cores, and ``radio-quiet'' Seyferts, in which the majority of the radio emission can be attributed to star-formation in the host galaxy. No significant difference is seen between the IR and optical spectroscopic properties of Seyferts with and without radio cores. (Abridged)

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arXiv2001

Mid-IR and CO Observations of the IR/X-Ray Luminous Seyfert I Galaxy NGC985: The Making or Breaking of a ULIRG?

We describe ISO and BIMA observations of the z=0.04 Seyfert 1 ring galaxy NGC985 which suggest close parallels with some quasar host galaxies. NGC985 contains two closely spaced nuclei embedded in an R$^{1/4}$--law stellar bulge and an outer ring, evidence of an ongoing merger. The system contains \~1.8x10^{10}Msolar of highly disturbed molecular gas which lies in an asymmetric bar-like structure with the peak in observed CO column densities significantly offset from the compact double nucleus. In contrast to this, the ISO observations show strong dust emission centered on the AGN, located in one of the two nuclei. Fainter CO, MIR, and radio continuum emission provide a glimpse of the complexities of star formation in the outer ring. An analysis of the kinematics of the main CO emission reveal evidence for two dynamically distinct molecular components within NGC985. The first is a set of isolated super-giant molecular clouds (SGMCs) which are concentrated within 9-10kpc of the active nucleus. Although randomly distributed about the center, the clouds may form part of a clumpy highly-disturbed disk which may be either just forming around double-nucleus (the making of a ULIRG), or alternatively may be in the process of being disrupted-perhaps as a result of a powerful nuclear outflow (the breaking of a ULIRG). A second major concentration of CO lies offset from the double-nucleus in a dynamically coherent ridge of emission in which powerful star formation is occurring. We tentatively associate CO emission with two out of six UV absorption-lines seen in the blue wing of the very broad Lyman alpha emission. Such an association would imply a complex inter-relationship between the nuclear CO cloud population in colliding systems, and AGN-driven winds.

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arXiv2001

HST Observations of Young Star Clusters in Interacting Galaxies

We present early results from the analysis of HST imaging observations for several pairs of interacting galaxies. We include two cases that were specifically chosen to represent a strong early (young) encounter (Arp 81 = NGC 6621/6622) and a weak late (old) encounter (Arp 297 = NGC 5752/5754). The goals of the project include a determination of the timing, frequency, strength, and characteristics of the young star clusters formed in these two limiting cases of tidal encounters.

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arXiv1999

Smoke in the "Smoke Rings": ISO Observations of Dust in Collisional Ring Galaxies

Collisional ring galaxies probably result from a head-on collision between a compact companion galaxy and a gas-rich disk system. We present a review of the discovery of warm dust in five collisional rings observed by ISO which range in total Far-IR luminosity from 10$^{10}$~ $<$ ~L$_{FIR}$ ~$<$ ~10$^{11}$ L$\odot$. The results show that in most cases, the mid-IR (MIR) flux is often a significant fraction of the total energy budget of star formation activity in these galaxies (at least 10% even in the least powerful cases). We argue that the MIR emission, when combined with optical and radio observations, allows us to build a more complete picture of activity in these collisional systems. Although not as extreme as ULIRGs, these collisional systems provide low-redshift examples of the early effects of galaxy collisions on the ISM and may be relevant to the collisional assembly of galaxy disk components at high redshift.

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arXiv1999

Plasma and Warm Dust in the Collisional Ring Galaxy VIIZw466 from VLA and ISO Observations

We present the first mid-infrared (Mid-IR) ($\lambda5-15μ$m) and radio continuum ($λλ$20,~6 and 3.6 cm) observations of the star-forming collisional ring galaxy VII Zw 466 and its host group made with the Infrared Space Observatory and the NRAO Very Large Array. A search was also made for CO line emission in two of the galaxies with the Onsala 20m radio telescope and upper limits were placed on the mass of molecular gas in those galaxies. The ring galaxy is believed to owe its morphology to a slightly off-center collision between an `intruder' galaxy and a disk. An off-center collision is predicted to generate a radially expanding density wave in the disk which should show large azimuthal variations in overdensity, and have observational consequences. The radio continuum emission shows the largest asymmetry, exhibiting a crescent-shaped distribution consistent with either the trapping of cosmic-ray particles in the target disk, or an enhanced supernova rate in the compressed region. On the other hand, the ISO observations (especially those made at $\lambda9.6μ$m) show a more scattered distribution, with emission centers associated with powerful star formation sites distributed more uniformly around the ring. Low-signal to noise observations at $\lambda15.0μ$m show possible emission inside the ring, with little emission directly associated with the \ion{H}{2} regions. The observations emphasize the complex relationship between the generation of radio emission and the development of star formation even in relatively simple and well understood collisional scenarios.

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arXiv1999

The HI and Ionized Gas Disk of the Seyfert Galaxy NGC 1144 = Arp 118: A Violently Interacting Galaxy with Peculiar Kinematics

We present observations of the distribution and kinematics of neutral and ionized gas in NGC 1144, a galaxy that forms part of the Arp 118 system. Ionized gas is present over a huge spread in velocity (1100 km/s) in the disk of NGC 1144, but HI emission is detected over only 1/3 of this velocity range, in an area that corresponds to the NW half of the disk. In the nuclear region of NGC 1144, a jump in velocity in the ionized gas component of 600 km/s is observed. Faint, narrow HI absorption lines are also detected against radio sources in the SE part of the disk of NGC 1144, which includes regions of massive star formation and a Seyfert nucleus. The peculiar HI distribution, which is concentrated in the NW disk, seems to be the inverse of the molecular distribution which is concentrated in the SE disk. Although this may partly be the result of the destruction of HI clouds in the SE disk, there is circumstantial evidence that the entire HI emission spectrum of NGC 1144 is affected by a deep nuclear absorption line covering a range of 600 km/s, and is likely blueshifted with respect to the nucleus. In this picture, a high column-density HI stream is associated with the nuclear ionized gas velocity discontinuity, and the absorption effectively masks any HI emission that would be present in the SE disk of NGC 1144.

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