Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userResolved Structure of Arp 220 Nuclei at lambda ~3 mm
130
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We analyze 3 mm emission of the ultraluminous infrared galaxy Arp 220 for spatially-resolved structure and spectral properties of the merger nuclei. ALMA archival data at ~0.05 resolution are used for extensive visibility fitting and deep imaging of continuum emission. The data are fitted well with two concentric components for each nucleus, such as two Gaussians or one Gaussian plus one exponential disk. The larger components in individual nuclei are similar in shape and extent, ~100-150 pc, to the cm-wave emission due to supernovae. They are therefore identified with the known starburst nuclear disks. The smaller components in both nuclei have about a few 10 pc sizes and peak brightness temperatures (Tb) more than twice higher than in previous single-Gaussian fitting. They correspond to the dust emission that we find centrally concentrated in both nuclei by subtracting the plasma emission measured at 33 GHz. The dust emission in the western nucleus is found to have a peak Tb ~ 530 K and a full width at half maximum of about 20 pc. This component is estimated to have a bolometric luminosity on the order of 10^{12.5} Lsun and a 20 pc-scale luminosity surface density 10^{15.5} Lsun/kpc^2. A luminous AGN is a plausible energy source for these high values while other explanations remain to be explored. Our continuum image also reveals a third structural component of the western nucleus --- a pair of faint spurs perpendicular to the disk major axis. We attribute it to a bipolar outflow from the highly inclined (i ~ 60 deg) western nuclear disk.
rate research
Read More
We observed with ALMA three deeply buried nuclei in two galaxies, NGC 4418 and Arp 220, at $sim$0.2$$ resolution over a total bandwidth of 67 GHz in $f_{rm rest}$ = 215 - 697 GHz. Here we (1) introduce our program, (2) describe our data reduction method for wide-band, high-resolution imaging spectroscopy, (3) analyze in visibilities the compact nuclei with line forests, (4) develop a continuum-based estimation method of dust opacity and gas column density in heavily obscured nuclei, which uses the BGN (buried galactic nuclei) model and is sensitive to $log(N_{rm H_2}/{rm cm}^{-2}) sim $ 25 - 26 at $lambda sim 1$ mm, and (5) present the continuum data and diagnosis of our targets. The three continuum nuclei have major-axis FWHM of $sim$0.1$$-0.3$$ (20-140 pc) aligned to their rotating nuclear disks of molecular gas. However, each nucleus is described better with two or three concentric components than with a single Gaussian. The innermost cores have sizes of 0.05$$-0.10$$ (8-40 pc), peak brightness temperatures of ~100-500 K at 350 GHz, and more fractional flux at lower frequencies. The intermediate components correspond to the nuclear disks. They have axial ratios of $approx$0.5 and hence inclinations $stackrel{>}{sim} 60$ deg. The outermost elements include the bipolar outflow from Arp 220W. We estimate 1 mm dust opacity of $tau_{rm d,1mm} approx 2.2$, $1.2$, and $stackrel{<}{sim} 0.4$ respectively for NGC 4418, Arp 220W, and Arp 220E. The first two correspond to $log(N_{rm H}/{rm cm}^{-2}) sim 26$ for conventional dust-opacity laws, and hence the nuclei are highly Compton thick.
We present the first aperture synthesis unbiased spectral line survey toward an extragalactic object. The survey covered the 40 GHz frequency range between 202 and 242 GHz of the 1.3 mm atmospheric window. We find that 80% of the observed band shows molecular emission, with 73 features identified from 15 molecular species and 6 isotopologues. The 13C isotopic substitutions of HC3N and transitions from H2(18)O, 29SiO, and CH2CO are detected for the first time outside the Galaxy. Within the broad observed band, we estimate that 28% of the total measured flux is due to the molecular line contribution, with CO only contributing 9% to the overall flux. We present maps of the CO emission at a resolution of 2.9x1.9 which, though not enough to resolve the two nuclei, recover all the single-dish flux. The 40 GHz spectral scan has been modelled assuming LTE conditions and abundances are derived for all identified species. The chemical composition of Arp 220 shows no clear evidence of an AGN impact on the molecular emission but seems indicative of a purely starburst-heated ISM. The overabundance of H2S and the low isotopic ratios observed suggest a chemically enriched environment by consecutive bursts of star formation, with an ongoing burst at an early evolutionary stage. The large abundance of water (~10^-5), derived from the isotopologue H2(18)O, as well as the vibrationally excited emission from HC3N and CH3CN are claimed to be evidence of massive star forming regions within Arp 220. Moreover, the observations put strong constraints on the compactness of the starburst event in Arp 220. We estimate that such emission would require ~2-8x10^6 hot cores, similar to those found in the Sgr B2 region in the Galactic center, concentrated within the central 700 pc of Arp 220.
We present the results of interferometric spectral line observations of Arp 220 at 3.5mm and 1.2mm from the Plateau de Bure Interferometer (PdBI), imaging the two nuclear disks in H$^{13}$CN$(1 - 0)$ and $(3 - 2)$, H$^{13}$CO$^+(1 - 0)$ and $(3 - 2)$, and HN$^{13}$C$(3 - 2)$ as well as SiO$(2 - 1)$ and $(6 - 5)$, HC$^{15}$N$(3 - 2)$, and SO$(6_6 - 5_5)$. The gas traced by SiO$(6 - 5)$ has a complex and extended kinematic signature including a prominent P Cygni profile, almost identical to previous observations of HCO$^+(3 - 2)$. Spatial offsets $0.1$ north and south of the continuum centre in the emission and absorption of the SiO$(6 - 5)$ P Cygni profile in the western nucleus (WN) imply a bipolar outflow, delineating the northern and southern edges of its disk and suggesting a disk radius of $sim40$ pc, consistent with that found by ALMA observations of Arp 220. We address the blending of SiO$(6 - 5)$ and H$^{13}$CO$^+(3 - 2)$ by considering two limiting cases with regards to the H$^{13}$CO$^+$ emission throughout our analysis. Large velocity gradient (LVG) modelling is used to constrain the physical conditions of the gas and to infer abundance ratios in the two nuclei. Our most conservative lower limit on the [H$^{13}$CN]/[H$^{13}$CO$^+$] abundance ratio is 11 in the WN, cf. 0.10 in the eastern nucleus (EN). Comparing these ratios to the literature we argue on chemical grounds for an energetically significant AGN in the WN driving either X-ray or shock chemistry, and a dominant starburst in the EN.
We report high resolution imaging of the ultraluminous infrared galaxy Arp 220 at 1.1, 1.6, and 2.22 microns with NICMOS on the HST. The diffraction-limited images at 0.1--0.2 arcsecond resolution clearly resolve both nuclei of the merging galaxy system and reveal for the first time a number of luminous star clusters in the circumnuclear envelope. The morphologies of both nuclei are strongly affected by dust obscuration, even at 2.2 microns : the primary nucleus (west) presents a crescent shape, concave to the south and the secondary (eastern) nucleus is bifurcated by a dust lane with the southern component being very reddened. In the western nucleus, the morphology of the 2.2 micron emission is most likely the result of obscuration by an opaque disk embedded within the nuclear star cluster. The morphology of the central starburst-cluster in the western nucleus is consistent with either a circumnuclear ring of star formation or a spherical cluster with the bottom half obscured by the embedded dust disk. Comparison of cm-wave radio continuum maps with the near-infrared images suggests that the radio nuclei lie in the dust disk on the west and near the highly reddened southern component of the eastern complex. The radio nuclei are separated by 0.98 arcseconds (corresponding to 364 pc at 77 Mpc) and the half-widths of the infrared nuclei are approximately 0.2-0.5 arcseconds. At least 8, unresolved infrared sources -- probably globular clusters -- are also seen in the circumnuclear envelope at radii 2-7 arcseconds . Their near-infrared colors do not significantly constrain their ages.
We present the first very-long-baseline interferometry (VLBI) detections of Zeeman splitting in another galaxy. We used Arecibo Observatory, the Green Bank Telescope, and the Very Long Baseline Array to perform dual-polarization observations of OH maser lines in the merging galaxy Arp 220. We measured magnetic fields of $sim$1-5 mG associated with three roughly parsec-sized clouds in the nuclear regions of Arp 220. Our measured magnetic fields have comparable strengths and the same direction as features at the same velocity identified in previous Zeeman observations with Arecibo alone. The agreement between single dish and VLBI results provides critical validation of previous Zeeman splitting observations of OH megamasers that used a single large dish. The measured magnetic field strengths indicate that magnetic energy densities are comparable to gravitational energy in OH maser clouds. We also compare our total intensity results to previously published VLBI observations of OH megamasers in Arp 220. We find evidence for changes in both structure and amplitude of the OH maser lines that are most easily explained by variability intrinsic to the masing region, rather than variability produced by interstellar scintillation. Our results demonstrate the potential for using high-sensitivity VLBI to study magnetic fields on small spatial scales in extragalactic systems.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
