We present 12CO (2-1) data of three Virgo spirals -- NGC 4330, NGC 4402 and NGC 4522 obtained using the Submillimeter Array. These three galaxies show clear evidence of ram pressure stripping due to ...the cluster medium as found in previous H i imaging studies. Using the high-resolution CO data, we investigate how the properties of the inner molecular gas disc change while a galaxy is undergoing H i stripping in the cluster. At given sensitivity limits, we do not find any clear signs of molecular gas stripping. However, both its morphology and kinematics appear to be quite disturbed as those of H i. Morphological peculiarities present in the molecular and atomic gas are closely related with each other, suggesting that the molecular gas can be also affected by strong intracluster medium (ICM) pressure even if it is not stripped. CO is found to be modestly enhanced along the upstream sides in these galaxies, which may change the local star formation activity in the disc. Indeed, the distribution of H alpha emission, a tracer of recent star formation, well coincides with that of the molecular gas, revealing enhancements near the local CO peak or along the CO compression. FUV and H alpha share some properties in common, but FUV is always more extended than CO/H alpha in the three galaxies, implying that the star-forming disc is rapidly shrinking as the molecular gas properties have changed. We discuss how ICM pressure affects dense molecular gas and hence star formation properties while diffuse atomic gas is being removed from a galaxy.
AT2018cow: A Luminous Millimeter Transient Ho, Anna Y. Q.; Phinney, E. Sterl; Ravi, Vikram ...
The Astrophysical journal,
01/2019, Letnik:
871, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present detailed submillimeter- through centimeter-wave observations of the extraordinary extragalactic transient AT2018cow. The apparent characteristics-the high radio luminosity, the rise and ...long-lived emission plateau at millimeter bands, and the sub-relativistic velocity-have no precedent. A basic interpretation of the data suggests coupled to a fast but sub-relativistic ( ) shock in a dense ( ) medium. We find that the X-ray emission is not naturally explained by an extension of the radio-submm synchrotron spectrum, nor by inverse Compton scattering of the dominant blackbody UV/optical/IR photons by energetic electrons within the forward shock. By , the X-ray emission shows spectral softening and erratic inter-day variability. Taken together, we are led to invoke an additional source of X-ray emission: the central engine of the event. Regardless of the nature of this central engine, this source heralds a new class of energetic transients shocking a dense medium, which at early times are most readily observed at millimeter wavelengths.
The Molecular Clouds of M31 Lada, Charles J.; Forbrich, Jan; Petitpas, Glen ...
The Astrophysical journal,
05/2024, Letnik:
966, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Abstract Deep interferometric observations of CO and dust continuum emission are obtained with the Submillimeter Array at 230 GHz to investigate the physical nature of the giant molecular cloud (GMC) ...population in the Andromeda galaxy (M31). We use J = 2 − 1 12 CO and 13 CO emission to derive the masses, sizes, and velocity dispersions of 162 spatially resolved GMCs. We perform a detailed study of a subset of 117 GMCs that exhibit simple, single-component line profile shapes. Examining the Larson scaling relations for these GMCs, we find (1) a highly correlated mass–size relation in both 12 CO and 13 CO emission; (2) a weakly correlated 12 CO line width–size (LWS) relation along with a weaker, almost nonexistent, 13 CO LWS relation, suggesting a possible dependence of the LWS relation on spatial scale; and (3) that only 43% of these GMCs are gravitationally bound. We identify two classes of GMCs based on the strength and extent of their 13 CO emission. Examination of the Larson relations finds that both classes are individually characterized by strong 12 CO mass–size relations and much weaker 12 CO and 13 CO LWS relations. The majority (73%) of strong 13 CO-emitting GMCs are found to be gravitationally bound. However, only 25% of the weak 13 CO-emitting GMCs are bound. The resulting breakdown in the Larson relations in the weak 13 CO-emitting population decouples the mass–size and LWS relations, demonstrating that independent physical causes are required to understand the origin of each. Finally, in nearly every aspect, the physical properties of the M31 GMCs are found to be very similar to those of local Milky Way clouds.
We present new high-resolution ALMA (13CO J = 1−0 and J = 2−1) and CARMA (12CO and 13CO J = 1−0) observations of two luminous infrared galaxies (LIRGs), Arp 55 and NGC 2623. The new data are ...complementary to published and archival submillimeter array observations of 12CO J = 2−1 and J = 3−2. We perform a Bayesian likelihood non-local thermodynamic equilibrium analysis to constrain the molecular gas physical conditions such as temperature, column, and volume densities and the 12CO/13CO abundance ratio. For Arp 55, an early/intermediate-staged merger, the line measurements are consistent with cold (∼10-20 K), dense (> cm−3) molecular gas. For NGC 2623, the molecular gas is warmer (∼110 K) and less dense ( cm−3). Because Arp 55 is an early/intermediate stage merger, while NGC 2623 is a merger remnant, the difference in physical conditions may be an indicator of merger stage. Comparing the temperature and volume density of several LIRGs shows that the molecular gas, averaged over ∼kiloparsec scales, of advanced mergers is in general warmer and less dense than early/intermediate stage mergers. We also find that the 12CO/13CO abundance ratio of NGC 2623 is unusually high (>250) when compared with the Milky Way; however, it follows a trend seen with other LIRGs in the literature. This high 12CO/13CO value is very likely due to stellar nucleosynthesis enrichment of the interstellar medium. On the other hand, Arp 55 has a more Galactic 12CO/13CO value with the most probable 12CO/13CO value being 20-30. We measure the CO-to-H2 conversion factor, , to be ∼0.1 and ∼0.7 (3 × 10−4/ ) M (K km s−1 pc2)−1 for Arp 55 and NGC 2623, respectively. Because Arp 55 is an early/intermediate-stage merger, this suggests that the transition from a Galactic conversion factor to a LIRG value happens at an even earlier merger stage.
We report the first detection of radio polarization of a gamma-ray burst (GRB) afterglow with the first intensive combined use of telescopes in the millimeter and submillimeter ranges for GRB ...171205A. The linear polarization degree in the millimeter band at the subpercent level (0.27% 0.04%) is lower than those observed in late-time optical afterglows (weighted average of ∼1%). The Faraday depolarization by nonaccelerated, cool electrons in the shocked region is one of the possible mechanisms for the low value. This scenario requires a total energy that is larger by a factor of ∼10 than ordinary estimates without considering nonaccelerated electrons. The polarization position angle varies by at least 20° across the millimeter band, which is not inconsistent with this scenario. This result indicates that polarimetry in the millimeter and submillimeter ranges is a unique tool for investigating GRB energetics, and coincident observations with multiple frequencies or bands would provide more accurate measurements of the nonaccelerated electron fraction.
We present the first radio polarimetric observations of a fast-rising blue optical transient, AT2018cow. Two epochs of polarimetry with additional coincident photometry were performed with the ...Atacama Large Millimeter/submillimeter Array. The overall photometric results based on simultaneous observations in the 100 and 230 GHz bands are consistent with the nonthermal radiation model reported by Ho et al. and indicate that the spectral peaks (∼110 GHz at the first epoch and ∼67 GHz at the second epoch) represent the synchrotron self-absorption frequency. The non-detection of linear polarization with <0.15% in the 230 GHz band at the phase when the effect of synchrotron self-absorption was quite small in the band may be explained by internal Faraday depolarization with high circumburst density and strong magnetic field. This result supports the stellar explosion scenario rather than the tidal disruption model. The maximum energy of accelerating particles at the shocks of AT2018cow-like objects is also discussed.
We present new data obtained with the Submillimeter Array for a sample of 14 nearby luminous and ultraluminous infrared galaxies. The galaxies were selected to have distances image Mpc and ...far-infrared luminosities image. The galaxies were observed with spatial resolutions of order 1 kpc in the CO image, CO image, super(13)CO image, and HCO super(+) image lines as well as the continuum at 880 mum and 1.3 mm. We have combined our CO and continuum data to measure an average gas-to-dust mass ratio of image (rms deviation 109) in the central regions of these galaxies, very similar to the value of 150 determined for the Milky Way. This similarity is interesting given the more intense heating from the starburst and possibly accretion activity in the luminous infrared galaxies compared to the Milky Way. We find that the peak H sub(2) surface density correlates with the far-infrared luminosity, which suggests that galaxies with higher gas surface densities inside the central kiloparsec have a higher star formation rate. The lack of a significant correlation between total H sub(2) mass and far-infrared luminosity in our sample suggests that the increased star formation rate is due to the increased availability of molecular gas as fuel for star formation in the central regions. In contrast to previous analyses by other authors, we do not find a significant correlation between central gas surface density and the star formation efficiency, as traced by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that it is the star formation rate, not the star formation efficiency, that increases with increasing central gas surface density in these galaxies.
Abstract
We have used the Submillimeter Array (SMA) at 860 $\mu$m to observe the brightest sources in the Submillimeter Common User Bolometer Array-2 (SCUBA-2) Cosmology Legacy Survey (S2CLS). The ...goal of this survey is to exploit the large field of the S2CLS along with the resolution and sensitivity of the SMA to construct a large sample of these rare sources and to study their statistical properties. We have targeted 70 of the brightest single-dish SCUBA-2 850 $\mu$m sources down to S850 ≈ 8 mJy, achieving an average synthesized beam of 2.4 arcsec and an average rms of σ860 = 1.5 mJy beam−1 in our primary beam-corrected maps. We searched our SMA maps for 4σ peaks, corresponding to S860 ≳ 6 mJy sources, and detected 62, galaxies, including three pairs. We include in our study 35 archival observations, bringing our sample size to 105 bright single-dish submillimetre sources with interferometric follow-up. We compute the cumulative and differential number counts, finding them to overlap with previous single-dish survey number counts within the uncertainties, although our cumulative number count is systematically lower than the parent S2CLS cumulative number count by 14 ± 6 per cent between 11 and 15 mJy. We estimate the probability that a ≳10 mJy single-dish submillimetre source resolves into two or more galaxies with similar flux densities to be less than 15 per cent. Assuming the remaining 85 per cent of the targets are ultraluminous starburst galaxies between z = 2 and 3, we find a likely volume density of ≳400 M⊙ yr−1 sources to be ${\sim }\,3^{+0.7}_{-0.6}\,{\times }\,10^{-7}$ Mpc−3. We show that the descendants of these galaxies could be ≳4 × 1011 M⊙ local quiescent galaxies, and that about 10 per cent of their total stellar mass would have formed during these short bursts of star formation.
We present moderate (∼5″) and high angular resolution (∼1″) observations of 12CO (J = 2 − 1) emission toward the nearby interacting galaxy NGC 3627 taken with the Submillimeter Array (SMA). These SMA ...mosaic maps of NGC 3627 reveal a prominent nuclear peak, inter-arm regions, and diffuse, extended emission in the spiral arms. A velocity gradient of ∼400-450 km s−1 is seen across the entire galaxy with velocity dispersions ranging from 80 km s−1 toward the nuclear region to 15 km s−1 in the spiral arms. We also detect unresolved 13CO (J = 2 − 1) line emission toward the nuclear region, southern bar end, and in a relatively isolated clump in the southern portion of the galaxy, while no C18O(J = 2 − 1) line emission is detected at a 3 rms noise level of 42 mJy beam−1 per 20 km s−1 channel. Using RADEX modeling with a large velocity gradient approximation, we derive kinetic temperatures ranging from ∼5 to 10 K (in the spiral arms) to ∼25 K (at the center) and H2 number densities from ∼400 to 1000 cm−3 (in the spiral arms) to ∼12,500 cm−3 (at the center). From this density modeling, we find a total H2 mass of 9.6 × 109 M , which is ∼50% higher than previous estimates made using a constant H2-CO conversion factor, but is largely dependent on the assumed vertical distribution of the CO gas. With the exception of the nuclear region, we also identify a tentative correlation between star formation efficiency and kinetic temperature. We derive a galactic rotation curve, finding a peak velocity of ∼207 km s−1 and estimate a total dynamical mass of 4.94 0.70 × 1010 M at a galactocentric radius of ∼6.2 kpc (121″).
Abstract
Interferometric observations have demonstrated that a significant fraction of single-dish submillimetre (submm) sources are blends of multiple submm galaxies (SMGs), but the nature of this ...multiplicity, i.e. whether the galaxies are physically associated or chance projections, has not been determined. We performed spectroscopy of 11 SMGs in six multicomponent submm sources, obtaining spectroscopic redshifts for nine of them. For an additional two component SMGs, we detected continuum emission but no obvious features. We supplement our observed sources with four single-dish submm sources from the literature. This sample allows us to statistically constrain the physical nature of single-dish submm source multiplicity for the first time. In three $(3/7, \rm{ or}\,\,43^{+39 }_{ -33}\,\,\rm{per\,\,cent\,\,\,\,at\,\,95\,\,{per\,\,cent}\,\,confidence})$ of the single-dish sources for which the nature of the blending is unambiguous, the components for which spectroscopic redshifts are available are physically associated, whereas 4/7 $(57^{+33 }_{ -39} \text{ per cent})$ have at least one unassociated component. When components whose spectra exhibit continuum but no features and for which the photometric redshift is significantly different from the spectroscopic redshift of the other component are also considered, 6/9 $(67^{+26 }_{ -37} \text{ per cent})$ of the single-dish sources are comprised of at least one unassociated component SMG. The nature of the multiplicity of one single-dish source is ambiguous. We conclude that physically associated systems and chance projections both contribute to the multicomponent single-dish submm source population. This result contradicts the conventional wisdom that bright submm sources are solely a result of merger-induced starbursts, as blending of unassociated galaxies is also important.
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