Abstract
We estimate the amount of negative feedback energy injected into the interstellar medium (ISM) of the host galaxy of 3C 273, a prototypical radio-loud quasar. We obtained 93, 233, and 343 ...GHz continuum images with the Atacama Large Millimeter/submillimeter Array (ALMA). After self-calibration and point-source subtraction, we reach an image dynamic range of ∼85,000 at 93 GHz, ∼39,000 at 233 GHz, and ∼2500 at 343 GHz. These are currently the highest image dynamic range obtained using ALMA. We detect spatially extended millimeter emission associated with the host galaxy, cospatial with the extended emission line region (EELR) observed in the optical. The millimeter spectral energy distribution and comparison with centimeter data show that the extended emission cannot be explained by dust thermal emission or synchrotron or thermal bremsstrahlung arising from massive star formation. We interpret the extended millimeter emission as thermal bremsstrahlung from gas directly ionized by the central source. The extended flux indicates that at least ∼7% of the bolometric flux of the nuclear source was used to ionize atomic hydrogen in the host galaxy. The ionized gas is estimated to be as massive as 10
10
–10
11
M
⊙
, but the molecular gas fraction with respect to the stellar mass is consistent with other ellipticals, suggesting that direct ionization ISM by the QSO may not be sufficient to suppress star formation, or we are witnessing a short timescale before negative feedback becomes observable. The discovery of a radio counterpart to EELRs provides a new pathway to studying the QSO–host ISM interaction.
The AKARI far-infrared all-sky survey maps Doi, Yasuo; Takita, Satoshi; Ootsubo, Takafumi ...
Publications of the Astronomical Society of Japan,
06/2015, Letnik:
67, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present a far-infrared all-sky atlas from a sensitive all-sky survey using the Japanese AKARI satellite. The survey covers > 99% of the sky in four photometric bands centred at 65 μm, 90 μm, 140 ...μm, and 160 μm, with spatial resolutions ranging from 1′ to 1
${^{\prime\prime}_{.}}$
5. These data provide crucial information on the investigation and characterisation of the properties of dusty material in the interstellar medium (ISM), since a significant portion of its energy is emitted between ∼ 50 and 200 μm. The large-scale distribution of interstellar clouds, their thermal dust temperatures, and their column densities can be investigated with the improved spatial resolution compared to earlier all-sky survey observations. In addition to the point source distribution, the large-scale distribution of ISM cirrus emission, and its filamentary structure, are well traced. We have made the first public release of the full-sky data to provide a legacy data set for use in the astronomical community.
Abstract
The tip of the tidal tail, resulting from an encounter between galaxies, features gas concentrations and some star-forming regions, such as tidal dwarf galaxies (TDGs). This region provides ...a unique laboratory for examining the star formation process in a dynamical environment distinct from that of disk galaxies. Using the Nobeyama 45 m telescope, we conducted
12
CO(1−0) position-switching observations at the tips of the southern tidal tail in the Antennae galaxies. We detected CO emission not only from the two star-forming TDG candidates but also in regions with no significant star formation. Adopting a Galactic CO-to-H
2
conversion factor without helium correction, the H
2
gas surface density is ∼5–12
M
⊙
pc
−2
. In most regions, the molecular-to-atomic gas ratio is around unity (0.6–1.9), but we find a region with a high ratio with a 3
σ
lower limit of >7.2. The star formation efficiency (SFE) of molecular gas is notably low (<0.15 Gyr
−1
), indicating less active star formation than in both nearby disk galaxies (∼0.5–1.0 Gyr
−1
) and other TDGs previously observed. Including previous observations, the molecular gas SFEs vary widely among TDGs/tidal tails, from 10
−2
to 10 Gyr
−1
, demonstrating significant variations in star formation activity. Potential factors contributing to the low SFE in the Antennae tail tips include extensive tides and/or the young age of the tail.
We present an initial result from the 12CO (J = 1-0) survey of 79 galaxies in 62 local luminous and ultraluminous infrared galaxy (LIRG and ULIRG) systems obtained using the 45 m telescope at the ...Nobeyama Radio Observatory. This is a systematic 12CO (J = 1-0) survey of the Great Observatories All-sky LIRGs Survey (GOALS) sample. The molecular gas mass of the sample is in the range within the central several kiloparsecs subtended by the beam. A method to estimate the size of a CO gas distribution is introduced, which is combined with the total CO flux in the literature. This method is applied to part of our sample, and we find that the median CO radius is 1-4 kpc. From the early stage to the late stage of mergers, we find that the CO size decreases while the median value of the molecular gas mass in the central several-kiloparsec region is constant. Our results statistically support a scenario where molecular gas inflows toward the central region from the outer disk to replenish gas consumed by starburst, and that such a process is common in merging LIRGs.
We present a giant molecular cloud (GMC) catalog of M33, containing 71 GMCs in total, based on wide-field and high-sensitivity CO(J = 3-2) observations with a spatial resolution of 100 pc using the ...ASTE 10 m telescope. Employing archival optical data, we identify 75 young stellar groups (YSGs) from the excess of the surface stellar density, and estimate their ages by comparing with stellar evolution models. A spatial comparison among the GMCs, YSGs, and H II regions enable us to classify GMCs into four categories: Type A, showing no sign of massive star formation (SF); Type B, being associated only with H II regions; Type C, with both H II regions and <10 Myr old YSGs; and Type D, with both H II regions and 10-30 Myr YSGs. Out of 65 GMCs (discarding those at the edges of the observed fields), 1 (1%), 13 (20%), 29 (45%), and 22 (34%) are Types A, B, C, and D, respectively. We interpret these categories as stages in a GMC evolutionary sequence. Assuming that the timescale for each evolutionary stage is proportional to the number of GMCs, the lifetime of a GMC with a mass >10 super(5) M sub(middot in circle) is estimated to be 20-40 Myr. In addition, we find that the dense gas fraction as traced by the CO(J = 3-2)/CO(J = 1-0) ratio is enhanced around SF regions. This confirms a scenario where dense gas is preferentially formed around previously generated stars, and will be the fuel for the next stellar generation. In this way, massive SF gradually propagates in a GMC until gas is exhausted.
We present an initial analysis of the properties of an all-sky image obtained by the Far-Infrared Surveyor (FIS) onboard the AKARI satellite, at 65 μm (N60), 90 μm (WIDE-S), 140 μm (WIDE-L), and 160 ...μm (N160). An absolute flux calibration was determined by comparing the data with COBE/DIRBE data sets; the intensity range was as wide as from a few MJy sr−1 to > 1 GJy sr−1. The uncertainties are considered to be the standard deviations with respect to the DIRBE data, and are less than 10% for intensities above 10, 3, 25, and 26 MJy sr−1 at the N60, WIDE-S, WIDE-L, and N160 bands, respectively. The characteristics of point sources in the image were also determined by stacking maps centred on photometric standard stars. The full width at half maxima of the point spread functions (PSFs) were 63″, 78″, and 88″ at the N60, WIDE-S, and WIDE-L bands, respectively. The PSF at the N160 band was not obtained due to the sensitivity, but it is thought to be the same as that of the WIDE-L one.
Abstract
We present a high-sensitivity (1
σ
< 1.6 mJy beam
−1
) continuum observation in a 343 arcmin
2
area of the northeast region of the Small Magellanic Cloud at a wavelength of 1.1 mm, ...conducted using the AzTEC instrument on the ASTE telescope. In the observed region, we identified 20 objects by contouring 10
σ
emission. Through spectral energy distribution analysis using 1.1 mm,
Herschel
, and
Spitzer
data, we estimated gas masses of 5 × 10
3
–7 × 10
4
M
⊙
, assuming a gas-to-dust ratio of 1000. The dust temperature and index of emissivity were also estimated as 18–33 K and 0.9–1.9, respectively, which are consistent with previous low-resolution studies. The dust temperature and the index of emissivity shows a weak negative linear correlation. We also investigated five CO-detected, dust-selected clouds in detail. The total gas masses were comparable to those estimated from the Mopra CO data, indicating that the assumed gas-to-dust ratio of 1000 and the
X
CO
factor of 1 × 10
21
cm
−2
(K km s
−1
)
−1
, with uncertainties of a factor of 2, are reliable for the estimation of the gas masses of molecular or dust-selected clouds. The dust column density showed good spatial correlation with CO emission, except for an object associated with bright young stellar objects. The 8
μ
m filamentary and clumpy structures also showed a spatial distribution similar to that of the CO emission and dust column density, supporting the fact that polycyclic aromatic hydrocarbon emissions arise from the surfaces of dense gas and dust clouds.
Abstract
We present the new single-dish CO (3–2) emission data obtained toward 19 early-stage and 7 late-stage nearby merging galaxies using the Atacama Submillimeter Telescope Experiment (ASTE). ...Combining with the single-dish and interferometric data of galaxies observed in previous studies, we investigate the relation between the CO (3–2) luminosity ($L^{\prime }_{\rm CO(3-2)}$) and the far-infrared luminosity (LFIR) in a sample of 29 early-stage and 31 late-stage merging galaxies, and 28 nearby isolated spiral galaxies. We find that normal isolated spiral galaxies and merging galaxies have different slopes (α) in the $\log L^{\prime }_{\rm CO(3-2)}$–log LFIR plane (α ∼ 0.79 for spirals and ∼1.12 for mergers). The large slope (α > 1) for merging galaxies can be interpreted as evidence for increasing star formation efficiency (SFE = $L_{\rm FIR}/L^{\prime }_{\rm CO(3-2)}$) as a function of LFIR. Comparing our results with sub-kpc-scale local star formation and global starburst activity in the high-z universe, we find deviations from the linear relationship in the $\log L^{\prime }_{\rm CO(3-2)}$–log LFIR plane for the late-stage mergers and high-z star-forming galaxies. Finally, we find that the average SFE gradually increases from isolated galaxies to merging galaxies and to high-z submillimeter galaxies/quasi-stellar objects. By comparing our findings with results from numerical simulations, we suggest that: (1) inefficient starbursts triggered by disk-wide dense clumps occur in the early stage of interaction, and (2) efficient starbursts triggered by central concentration of gas occur in the final stage. A systematic high spatial resolution survey of diffuse- and dense-gas tracers is the key to confirming this scenario.
ABSTRACT
The first 1.1 mm continuum survey toward the Small Magellanic Cloud (SMC) was performed using the AzTEC instrument installed on the ASTE 10 m telescope. This survey covered 4.5 deg
2
of the ...SMC with 1
σ
noise levels of 5–12 mJy beam
−1
, and 44 extended objects were identified. The 1.1 mm extended emission has good spatial correlation with
Herschel
160
μ
m, indicating that the origin of the 1.1 mm extended emission is thermal emission from a cold dust component. We estimated physical properties using the 1.1 mm and filtered
Herschel
data (100, 160, 250, 350, and 500
μ
m). The 1.1 mm objects show dust temperatures of 17–45 K and gas masses of 4 × 10
3
–3 × 10
5
M
⊙
, assuming single-temperature thermal emission from the cold dust with an emissivity index,
β
, of 1.2 and a gas-to-dust ratio of 1000. These physical properties are very similar to those of giant molecular clouds (GMCs) in our galaxy and the Large Magellanic Cloud. The 1.1 mm objects also displayed good spatial correlation with the
Spitzer
24
μ
m and CO emission, suggesting that the 1.1 mm objects trace the dense gas regions as sites of massive star formation. The dust temperature of the 1.1 mm objects also demonstrated good correlation with the 24
μ
m flux connected to massive star formation. This supports the hypothesis that the heating source of the cold dust is mainly local star-formation activity in the 1.1 mm objects. The classification of the 1.1 mm objects based on the existence of star-formation activity reveals the differences in the dust temperature, gas mass, and radius, which reflects the evolution sequence of GMCs.
Abstract
The conversion factor from carbon monoxide (CO) intensity to molecular gas mass is a source of large uncertainty in understanding gas and its relation to star formation in galaxies. In ...particular, the conversion factor in low-metallicity environments have remained elusive, as currently only two galaxies have been detected in any CO isotopes in environments with 12 + log (O$/$H) < 8.0. Here we report 12CO (J = 1–0) and 13CO (J = 1–0) observations towards a star-forming region in DDO 154, a low-metallicity dwarf irregular galaxy at 12 + log (O$/$H) = 7.67. This is a re-observation of a previous non-detection at higher angular and velocity resolution. No significant emission was detected. By estimating the molecular gas mass from associated star formation, we find that DDO 154 has a conversion factor of more than 103 times the Milky Way. Alternatively, if we estimate molecular mass using dust continuum emission, the conversion factor is at least 2 orders of magnitude larger than the Milky Way. These estimates signify a large amount of CO-dark molecular gas in this galaxy.
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