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Register a new userVLA H53alpha radio recombination line observations of the ultraluminous infrared galaxy Arp 220
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Added by
Carlos A. Rodriguez-Rico
Publication date
2005
fields
Physics
and research's language is
English
Authors
C. A. Rodriguez-Rico
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We present high angular resolution (0.7) observations made with the Very Large Array (VLA) of the radio recombination line (RRL) H53alpha and radio continuum emission at 43 GHz from the ultraluminous infrared galaxy (ULIRG) Arp 220. The 43 GHz continuum emission shows a compact structure (~2) with two peaks separated by ~1, the East (E) and West (W) components, that correspond to each galactic nucleus of the merger. The spectral indices for both the E and W components, using radio continuum images at 8.3 and 43 GHz are typical of synchrotron emission (alpha ~ -1.0). Our 43 GHz continuum and H53alpha line observations confirm the flux densities predicted by the models proposed by Anantharamaiah et al. This agreement with the models implies the presence of high-density (~ 100,000 cm^-3) compact HII regions (~ 0.1 pc) in Arp 220. The integrated H53alpha line emission is stronger toward the non-thermal radio continuum peaks, which are also coincident with the peaks of molecular emission of the H2CO. The coincidence between the integrated H53alpha and the H2CO maser line emission suggests that the recent star forming regions, traced by the high density gas, are located mainly in regions that are close to the two radio continuum peaks. A velocity gradient of ~ 0.30 km/s/pc in the H53alpha RRL is observed toward the E component and a second velocity gradient of ~ 0.15 km/s/pc is detected toward the W component. The orientations of these velocity gradients are in agreement with previous CO, HI and OH observations. The kinematics of the high-density ionized gas traced by the H53alpha line are consistent with two counter rotating disks as suggested by the CO and HI observations.
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We present observations of radio recombination lines from the starburst galaxy Arp 220 at 1.4, 8.1, 84, 96 and 207 GHz (sensitive upper limit for the 1.4 GHz line and firm detections at the other frequencies), and the radio continuum spectrum between 330 MHz and 207 GHz. We show that a model with three components of ionized gas with different densities and area covering factors can consistently explain both RRL and continuum data. The total mass of ionized gas in the three components is 3 x 10^7 M_sun requiring 3 x 10^5 O5 stars with a total Lyman continuum production rate (NLyc) of 1.3 x 10^{55} photons /s. These values imply a dust extinction A_V ~ 45 magnitudes and an SFR of ~240 M_sun/yr. The NLyc of ~3% associated with the high density HII regions implies similar SFR at recent epochs. The data is also consistent with multiple starbursts of very high SFR and short durations. The derived value of 24 for the IR-excess favours a starburst rather than an AGN as the origin of the observed FIR luminosity. (the abstract has been abridged)
We present MERLIN observations of the continuum (both 1.6 and 5 GHz) and OH maser emission towards Arp220. the correct spatial configuration of the various componnents of the galaxy is revealed. In the eastern component the masers are shown to be generally coincident with the larger scale continuum emission; in the west, the masers and continuum do not generally arise from the same location. A velocity gradient (0.32+/-0.03km/s/pc) is found in the eastern nuclear region in MERLIN scales; this gradient is three times smaller than seen in OH and implies that the OH gas lies inside the HI. A re-analysis of previously presented global VLBI data (Lonsdale et al. 1998) reveals a very high velocity gradient (18.67+/-0.12km/s/pc) in one component, possibly the site of a heavily obscured AGN.
We present observations in the H53alpha line and radio continuum at 43 GHz carried out with the VLA in the D array (2 angular resolution) toward the starburst galaxy NGC 5253. VLA archival data have been reprocessed to produce a uniform set of 2, 1.3 and 0.7 cm high angular (0.2 X 0.1) radio continuum images. The RRL H53alpha, a previously reported measurement of the H92alpha RRL flux density and the reprocessed high angular resolution radio continuum flux densities have been modeled using a collection of HII regions. Based on the models, the ionized gas in the nuclear source has an electron density of ~6 X 10^4 cm^-3 and an volume filling factor of 0.05. A Lyman continuum photon production rate of 2 X 10^52 s^-1 is necessary to sustain the ionization in the nuclear region. The number of required O7 stars in the central 1.5 pc of the supernebula is ~ 2000. The H53alpha velocity gradient 10 km s^-1 arcsec^-1) implies a dynamical mass of ~3X10^5 Msun; this mass suggests the supernebula is confined by gravity.
We conducted systematic observations of the H I Br$alpha$ (4.05 $mu$m) and Br$beta$ (2.63 $mu$m) lines in 52 nearby ($z<0.3$) ultraluminous infrared galaxies (ULIRGs) with AKARI. Among 33 ULIRGs wherein the lines are detected, three galaxies show anomalous Br$beta$/Br$alpha$ line ratios ($sim1.0$), which are significantly higher than those for case B (0.565). Our observations also show that ULIRGs have a tendency to exhibit higher Br$beta$/Br$alpha$ line ratios than those observed in Galactic H II regions. The high Br$beta$/Br$alpha$ line ratios cannot be explained by a combination of dust extinction and case B since dust extinction reduces the ratio. We explore possible causes for the high Br$beta$/Br$alpha$ line ratios and show that the observed ratios can be explained by a combination of an optically thick Br$alpha$ line and an optically thin Br$beta$ line. We simulated the H II regions in ULIRGs with the Cloudy code, and our results show that the high Br$beta$/Br$alpha$ line ratios can be explained by high-density conditions, wherein the Br$alpha$ line becomes optically thick. To achieve a column density large enough to make the Br$alpha$ line optically thick within a single H II region, the gas density must be as high as $nsim10^8$ $mathrm{cm}^{-3}$. We therefore propose an ensemble of H II regions, in each of which the Br$alpha$ line is optically thick, to explain the high Br$beta$/Br$alpha$ line ratio.
We present our new deep optical imaging and long-slit spectroscopy for Arp 220 that is the archetypical ULIRG in the local universe. Our sensitive Ha imaging has newly revealed large-scale, Ha absorption, i.e., post-starburst regions in this merger; one is found in the eastern superbubble and the other is in the two tidal tails that are clearly reveled in our deep optical imaging. The size of Ha absorption region in the eastern bubble is 5 kpc x 7.5 kpc and the observed Ha equivalent widths are ~2 A +- 0.2 A. The sizes of the northern and southern Ha-absorption tidal tails are ~5 kpc x 10 kpc and ~6 kpc x 20 kpc, respectively. The observed Ha equivalent widths range from 4 A to 7 A. In order to explain the presence of the two post-starburst tails, we suggest a possible multiple-merger scenario for Arp 220 in which two post-starburst disk-like structures merged into one, and then caused the two tails. This favors that Arp 220 is a multiple merging system composed of four or more galaxies, arising from a compact group of galaxies. Taking our new results into account, we discuss a star formation history in the last 1 Gyr in Arp 220.
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