arXiv subjects

Ryohei Kawabe

Publications and source records attributed to Ryohei Kawabe.

At least 55 records · Page 3Linked to original sources

arXiv2020

Super-resolution Imaging of the Protoplanetary Disk HD 142527 Using Sparse Modeling

With an emphasis on improving the fidelity even in super-resolution regimes, new imaging techniques have been intensively developed over the last several years, which may provide substantial improvements to the interferometric observation of protoplanetary disks. In this study, sparse modeling (SpM) is applied for the first time to observational data sets taken by the Atacama Large Millimeter/submillimeter Array (ALMA). The two data sets used in this study were taken independently using different array configurations at Band 7 (330 GHz), targeting the protoplanetary disk around HD 142527; one in the shorter-baseline array configuration (~ 430 m), and the other in the longer-baseline array configuration (~ 1570 m). The image resolutions reconstructed from the two data sets are different by a factor of ~ 3. We confirm that the previously known disk structures appear on the images produced by both SpM and CLEAN at the standard beam size. The image reconstructed from the shorter-baseline data using the SpM matches that obtained with the longer-baseline data using CLEAN, achieving a super-resolution image from which a structure finer than the beam size can be reproduced. Our results demonstrate that on-going intensive development in the SpM imaging technique is beneficial to imaging with ALMA.

astro-ph.EP↗

arXiv2020

Discovery of Radio Jets in Phoenix Galaxy Cluster Center

We report the results of the Australia Telescope Compact Array (ATCA) 15 mm observation of the Phoenix galaxy cluster possessing an extreme star-burst brightest cluster galaxy (BCG) at the cluster center. We spatially resolved radio emission around the BCG, and found diffuse bipolar and bar-shape structures extending from the active galactic nucleus (AGN) of the BCG. They are likely radio jets/lobes, whose sizes are ~10-20 kpc and locations are aligned with X-ray cavities. If we assume that the radio jets/lobes expand with the sound velocity, their ages are estimated to be ~10 Myr. We also found compact radio emissions near the center and suggest that they are another young bipolar jets with ~1 Myr of age. Moreover, we found extended radio emission surrounding the AGN and discussed the possibility that the component is a product of the cooling flow, by considering synchrotron radiation partially absorbed by molecular clumps, free-free emission from the warm ionized gas, and the spinning dust emission from dusty circum-galactic medium.

astro-ph.GA↗

arXiv2020

Wind- and Operation-Induced Vibration Measurements of the Main Reflector of the Nobeyama 45 m Radio Telescope

As deformations of the main reflector of a radio telescope directly affect the observations, the evaluation of the deformation is extremely important. Dynamic characteristics of the main reflector of the Nobeyama 45 m radio telescope, Japan, are measured under two conditions: The first is when the pointing observation is in operation, and the second is when the reflector is stationary and is subjected to wind loads when the observation is out of operation. Dynamic characteristics of the main reflector are measured using piezoelectric accelerometers. When the telescope is in operation, a vibration mode with one nodal line horizontally or vertically on the reflector is induced, depending on whether the reflector is moving in the azimuthal or elevational planes, whereas under windy conditions, vibration modes that have two to four nodal lines are simultaneously induced. The predominant mode is dependent on the direction of wind loads.

astro-ph.IM↗

arXiv2020

Model of a gap formed by a planet with fast inward migration

A planet is formed within a protoplanetary disk. Recent observations have revealed substructures such as gaps and rings, which may indicate forming planets within the disk. Due to disk--planet interaction, the planet migrates within the disk, which can affect a shape of the planet-induced gap. In this paper, we investigate effects of fast inward migration of the planet on the gap shape, by carrying out hydrodynamic simulations. We found that when the migration timescale is shorter than the timescale of the gap-opening, the orbital radius is shifted inward as compared to the radial location of the gap. We also found a scaling relation between the radial shift of the locations of the planet and the gap as a function of the ratio of the timescale of the migration and gap-opening. Our scaling relation also enables us to constrain the gas surface density and the viscosity when the gap and the planet are observed. Moreover, we also found the scaling relation between the location of the secondary gap and the aspect ratio. By combining the radial shift and the secondary gap, we may constrain the physical condition of the planet formation and how the planet evolves in the protoplanetary disk, from the observational morphology.

astro-ph.EP↗

arXiv2020

DESHIMA on ASTE: On-sky Responsivity Calibration of the Integrated Superconducting Spectrometer

We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter-bank and Microwave Kinetic Inductance Detector (MKID) to investigate dusty star-burst galaxies in the distant universe at millimeter and submillimeter wavelength. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV, 0.4-3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of $1σ=4$%, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs, and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array.

astro-ph.IM↗

arXiv2019

SOFIA/HAWC+ View of an Extremely Luminous Infrared Galaxy, WISE1013+6112

We present far-infrared (FIR) properties of an extremely luminous infrared galaxy (ELIRG) at $z_{\rm spec}$ = 3.703, WISE J101326.25+611220.1 (WISE1013+6112). This ELIRG is selected as an IR-bright dust-obscured galaxy (DOG) based on the photometry from the Sloan digital sky survey (SDSS) and wide-field infrared survey explorer (WISE). In order to derive its accurate IR luminosity, we perform follow-up observations at 89 and 154 $μ$m using the high-resolution airborne wideband camera-plus (HAWC+) on board the 2.7-m stratospheric observatory for infrared astronomy (SOFIA) telescope. We conduct spectral energy distribution (SED) fitting with CIGALE using 15 photometric data (0.4-1300 $μ$m). We successfully pin down FIR SED of WISE1013+6112 and its IR luminosity is estimated to be $L_{\rm IR}$ = (1.62 $\pm$ 0.08) $\times 10^{14}$ $L_{\odot}$, making it one of the most luminous IR galaxies in the universe. We determine the dust temperature of WISE1013+6112 is $T_{\rm dust}$ = 89 $\pm$ 3 K, which is significantly higher than that of other populations such as SMGs and FIR-selected galaxies at similar IR luminosities. The resultant dust mass is $M_{\rm dust}$ = (2.2 $\pm$ 0.1) $\times 10^{8}$ $M_{\odot}$. This indicates that WISE1013+6112 has a significant active galactic nucleus (AGN) and star-forming activity behind a large amount of dust.

astro-ph.GA↗

arXiv2019

Nobeyama 45-m Mapping Observations toward Orion A.I. Molecular Outflows

We conducted an exploration of 12CO molecular outflows in the Orion A giant molecular cloud to investigate outflow feedback using 12CO (J = 1-0) and 13CO (J = 1-0) data obtained by the Nobeyama 45-m telescope. In the region excluding the center of OMC 1, we identified 44 12CO (including 17 newly detected) outflows based on the unbiased and systematic procedure of automatically determining the velocity range of the outflows and separating the cloud and outflow components. The optical depth of the 12CO emission in the detected outflows is estimated to be approximately 5. The total momentum and energy of the outflows, corrected for optical depth, are estimated to be 1.6 x 10 2 M km s-1 and 1.5 x 10 46 erg, respectively. The momentum and energy ejection rate of the outflows are estimated to be 36% and 235% of the momentum and energy dissipation rates of the cloud turbulence, respectively. Furthermore, the ejection rates of the outflows are comparable to those of the expanding molecular shells estimated by Feddersen et al. (2018, ApJ, 862, 121). Cloud turbulence cannot be sustained by the outflows and shells unless the energy conversion efficiency is as high as 20%.

astro-ph.SR↗

arXiv2019

First light demonstration of the integrated superconducting spectrometer

Ultra-wideband 3D imaging spectrometry in the millimeter-submillimeter (mm-submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution. However, it is challenging to scale up conventional coherent heterodyne receivers or free-space diffraction techniques to sufficient bandwidths ($\geq$1 octave) and numbers of spatial pixels (>$10^2$). Here we present the design and first astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer, which covers 332-377 GHz with a spectral resolution of $F/ΔF \sim 380$. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs) with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine, and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to $\sim$1.1 THz. The miniature chip footprint of a few $\mathrm{cm^2}$ allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible.

astro-ph.IM↗

arXiv2019

Nobeyama 45-m mapping observations toward nearby molecular clouds, Orion A, Aquila Rift, and M17: Project overview

We carried out mapping observations toward three nearby molecular clouds, Orion A, Aquila Rift, and M17, using a new 100 GHz receiver, FOREST, on the Nobeyama 45-m telescope. In the present paper, we describe the details of the data obtained such as intensity calibration, data sensitivity, angular resolution, and velocity resolution. Each target contains at least one high-mass star-forming region. The target molecular lines were $^{12}$CO ($J = 1 - 0$), $^{13}$CO ($J = 1 - 0$), C$^{18}$O ($J = 1 - 0$), N$_2$H$^+$ ($J=1-0$), and CCS ($J_N=8_7-7_6$), with which we covered the density range of 10$^2$ cm$^{-3}$ to 10$^6$ cm$^{-3}$ with an angular resolution of $\sim 20\arcsec$ and a velocity resolution of $\sim$ 0.1 km s$^{-1}$. Assuming the representative distances of 414 pc, 436 pc, and 2.1 kpc, the maps of Orion A, Aquila Rift, and M17 cover most of the densest parts with areas of about 7 pc $\times$ 15 pc, 7 pc $\times$ 7 pc, and 36 pc $\times$ 18 pc, respectively. On the basis of the $^{13}$CO column density distribution, the total molecular masses are derived to be $3.86 \times 10^4 M_\odot$, $2.67 \times 10^4 M_\odot$, and $8.1\times 10^5 M_\odot$ for Orion A, Aquila Rift, and M17, respectively. For all the clouds, the H$_2$ column density exceeds the theoretical threshold for high-mass star formation of $\gtrsim$ 1 g cm$^{-2}$, only toward the regions which contain current high-mass star-forming sites. For other areas, further mass accretion or dynamical compression would be necessary for future high-mass star formation. This is consistent with the current star formation activity. Using the $^{12}$CO data, we demonstrate that our data have enough capability to identify molecular outflows, and for Aquila Rift, we identify 4 new outflow candidates. The scientific results will be discussed in details in separate papers.

astro-ph.GA↗

arXiv2019

Discovery of an au-scale excess in millimeter emission from the protoplanetary disk around TW Hya

We report the detection of an excess in dust continuum emission at 233~GHz (1.3~mm in wavelength) in the protoplanetary disk around TW~Hya revealed through high-sensitivity observations at $\sim$3~au resolution with the Atacama Large Millimeter/submillimeter Array (ALMA). The sensitivity of the 233~GHz image has been improved by a factor of 3 with regard to that of our previous cycle 3 observations. The overall structure is mostly axisymmetric, and there are apparent gaps at 25 and 41 au as previously reported. The most remarkable new finding is a few au-scale excess emission in the south-west part of the protoplanetary disk. The excess emission is located at 52 au from the disk center and is 1.5 times brighter than the surrounding protoplanetary disk at a significance of 12$σ$. We performed a visibility fitting to the extracted emission after subtracting the axisymmetric protoplanetary disk emission and found that the inferred size and the total flux density of the excess emission are 4.4$\times$1.0~au and 250~$μ$Jy, respectively. The dust mass of the excess emission corresponds to 0.03~$M_\oplus$ if a dust temperature of 18~K is assumed. Since the excess emission can also be marginally identified in the Band 7 image at almost the same position, the feature is unlikely to be a background source. The excess emission can be explained by a dust clump accumulated in a small elongated vortex or a massive circumplanetary disk around a Neptune mass forming-planet.

astro-ph.SR↗

arXiv2019

Nobeyama 45-m Mapping Observations toward Orion A. III. Multi-Line Observations toward an Outflow-shocked Region, OMC-2 FIR

We present the results of mapping observations toward an outflow-shocked region, OMC-2 FIR 4 using the Nobeyama 45-m telescope. We observed the area in $^{13}$CO ($J=1-0$), C$^{18}$O ($J=1-0$), N$_2$H$^+$ ($J=1-0$), CCS ($J_N=8_7-7_6$), HCO$^+$ ($J=1-0$), H$^{13}$CO$^+$ ($J=1-0$), HN$^{13}$C ($J=1-0$), H$^{13}$CN ($J=1-0$), DNC ($J=1-0$), N$_2$D$^+$ ($J=1-0$), and DC$_3$N ($J=9-8$). We detected a dense molecular clump that contains FIR 4/5. We also detected in $^{13}$CO blueshifted and redshifted components driven presumably by protostellar outflows in this region. The axes of the FIR 3 and VLA 13 outflows, projected on the plane of the sky, appear to point toward the FIR 4 clump, suggesting that the clump may be compressed by protostellar outflows from Class I sources, FIR 3 and VLA 13. Applying the hyperfine fit of N$_2$H$^+$ lines, we estimated the excitation temperature to be $\sim$ 20 K. The high excitation temperature is consistent with the fact that the clump contains protostars. The CCS emission was detected in this region for the first time. Its abundance is estimated to be a few $\times 10^{-12}$, indicating that the region is chemically evolved at $\sim 10^5$ years, which is comparable to the typical lifetime of the Class I protostars. This timescale is consistent with the scenario that star formation in FIR 4 is triggered by dynamical compression of the protostellar outflows. The [HNC]/[HCN] ratio is evaluated to be $\sim 0.5$ in the dense clump and the outflow lobes, whereas it is somewhat larger in the envelope of the dense clump. The small [HNC]/[HCN] ratio indicates that the HNC formation was prevented due to high temperatures. Such high temperatures seem to be consistent with the scenario that either protostellar radiation or outflow compression, or both, affected the thermal properties of this region.

astro-ph.SR↗

arXiv2019

First [NII]122$μ$m line detection in a QSO-SMG pair BRI 1202-0725 at $z=4.69$

We report the first detection obtained with ALMA of the [N II] 122$μ$m line emission from a galaxy group BRI 1202-0725 at $z=4.69$ consisting of a QSO and a submilimeter-bright galaxy (SMG). Combining with a detection of [N II] 205$μ$m line in both galaxies, we constrain the electron densities of the ionized gas based on the line ratio of [NII]122/205. The derived electron densities are $26^{+12}_{-11}$ and $134^{+50}_{-39}$ cm$^{-3}$ for the SMG and the QSO, respectively. The electron density of the SMG is similar to that of the Galactic Plane and to the average of the local spirals. Higher electron densities by up to a factor of three could, however, be possible for systematic uncertainties of the line flux estimates. The electron density of the QSO is comparable to high-$z$ star-forming galaxies at $z=1.5-2.3$, obtained using rest-frame optical lines and with the lower limits suggested from stacking analysis on lensed starbursts at $z=1-3.6$ using the same tracer of [NII]. Our results suggest a large scatter of electron densities in global scale at fixed star formation rates for extreme starbursts. The success of the [N II] 122$μ$m and 205$μ$m detections at $z=4.69$ demonstrates the power of future systematic surveys of extreme starbursts at $z>4$ for probing the ISM conditions and the effects on surrounding environments.

astro-ph.GA↗

arXiv2019

A Radio-to-millimeter Census of Star-forming Galaxies in Protocluster 4C~23.56 at z = 2.5 : Global and local gas kinematics

We present a study of the gas kinematics of star-forming galaxies associated with protocluster 4C 23.56 at $z=2.49$ using $0''.4$ resolution CO (4-3) data taken with ALMA. Eleven H$α$ emitters (HAEs) are detected in CO (4-3), including six HAEs that were previously detected in CO (3-2) at a coarser angular resolution. The detections in both CO lines are broadly consistent in the line widths and the redshifts, confirming both detections. With an increase in the number of spectroscopic redshifts, we confirm that the protocluster is composed of two merging groups with a total halo mass of $\log{(M_{\rm cl}/M_{\odot})} =13.4-13.6$, suggesting that the protocluster would evolve into a Virgo-like cluster ($>10^{14} M_{\odot}$). We compare the CO line widths and the CO luminosities with galaxies in other (proto)clusters ($n_{\rm gal}=91$) and general fields ($n_{\rm gal}=80$) from other studies. The 4C23.56 protocluster galaxies have CO line widths and luminosities comparable to other protocluster galaxies on average. On the other hand, the CO line widths are on average broader by $\approx50\%$ compared to field galaxies, while the median CO luminosities are similar. The broader line widths can be attributed to both effects of unresolved gas-rich mergers and/or compact gas distribution, which is supported by our limited but decent angular resolution observations and the size estimate of three galaxies. Based on these results, we argue that gas-rich mergers may play a role in the retention of the specific angular momentum to a value similar to that of field populations during cluster assembly, though we need to verify this with a larger number of samples.

astro-ph.GA↗

arXiv2019

Nobeyama 45 m Mapping Observations toward Orion A. II. Classification of cloud structures and variation of the $^{13}$CO/C$^{18}$O abundance ratio due to far-UV Radiation

We present results of the classification of cloud structures toward the Orion A Giant Molecular Cloud based on wide-field $^{12}$CO ($J$ = 1--0), $^{13}$CO ($J$ = 1-0), and C$^{18}$O ($J$ = 1-0) observations using the Nobeyama 45 m radio telescope. We identified 78 clouds toward Orion A by applying Spectral Clustering for Interstellar Molecular Emission Segmentation (SCIMES) to the data cube of the column density of $^{13}$CO. Well-known subregions such as OMC-1, OMC-2/3, OMC-4, OMC-5, NGC 1977, L1641-N, and the dark lane south filament (DLSF) are naturally identified as distinct structures in Orion A. These clouds can also be classified into three groups: the integral-shaped filament, the southern regions of Orion A, and the other filamentary structures in the outer parts of Orion A and the DLSF. These groups show differences in scaling relations between the physical properties of the clouds. We derived the abundance ratio between $^{13}$CO and C$^{18}$O, $X_{^{13}\mathrm{CO}}/X_{\mathrm{C}^{18}\mathrm{O}}$, which ranges from 5.6 to 17.4 on median over the individual clouds. The significant variation of $X_{^{13}\mathrm{CO}}/X_{\mathrm{C}^{18}\mathrm{O}}$ is also seen within a cloud in both of the spatial and velocity directions and the ratio tends to be high at the edge of the cloud. The values of $X_{^{13}\mathrm{CO}}/X_{\mathrm{C}^{18}\mathrm{O}}$ decrease from 17 to 10 with the median of the column densities of the clouds at the column density of $N_{\mathrm{C^{18}O}} \gtrsim 1 \times 10^{15}$ cm$^{-2}$ or visual extinction of $A_V \gtrsim 3$ mag under the strong far-ultraviolet (FUV) environment of $G_0 > 10^{3}$, whereas it is almost independent of the column density in the weak FUV radiation field. These results are explained if the selective photodissociation of C$^{18}$O is enhanced under a strong FUV environment and it is suppressed in the dense part of the clouds.

astro-ph.GA↗

arXiv2019

The Atacama Large Aperture Submillimeter Telescope (AtLAST)

The sub-mm sky is a unique window for probing the architecture of the Universe and structures within it. From the discovery of dusty sub-mm galaxies, to the ringed nature of protostellar disks, our understanding of the formation, destruction, and evolution of objects in the Universe requires a comprehensive view of the sub-mm sky. The current generation single-dish sub-mm facilities have shown of the potential for discovery, while interferometers have presented a high resolution view into the finer details. However, our understanding of large-scale structure and our full use of these interferometers is now hampered by the limited sensitivity of our sub-mm view of the universe at larger scales. Thus, now is the time to start planning the next generation of sub-mm single dish facilities, to build on these revolutions in our understanding of the sub-mm sky. Here we present the case for the Atacama Large Aperture Submillimeter Telescope (AtLAST), a concept for a 50m class single dish telescope. We envision AtLAST as a facility operating as an international partnership with a suite of instruments to deliver the transformative science described in many Astro2020 science white papers. A 50m telescope with a high throughput and 1$^\circ$ FoV with a full complement of advanced instrumentation, including highly multiplexed high-resolution spectrometers, continuum cameras and Integral Field Units, AtLAST will have mapping speeds thousands of times greater than any current or planned facility. It will reach confusion limits below $L_*$ in the distant universe and resolve low-mass protostellar cores at the distance of the Galactic Center, providing synergies with upcoming facilities across the spectrum. Located on the Atacama plateau, to observe frequencies un-obtainable by other observatories, AtLAST will enable a fundamentally new understanding of the sub-mm universe at unprecedented depths.

astro-ph.IM↗

arXiv2019

Astro2020 Science White Paper: Exploration and characterization of the earliest epoch of galaxy formation: beyond the re-ionization era

State-of-the-art rest-frame UV and FIR photometric and spectroscopic observations are now pushing the redshift frontiers of galaxy formation studies up to $z\sim9-11$ and beyond. Recent HST observations unveiled the presence of a star-forming galaxy exhibiting the Lyman break at $λ_{\rm obs}=1.47\pm0.01$ $μ$m, i.e., a $z=11.09^{+0.08}_{-0.12}$ galaxy with a stellar mass of $\sim10^9 M_\odot$, demonstrating that galaxy build-up was well underway early in the epoch of reionization (EoR) at $z>10$. Targeted spectroscopy of a lensed Lyman break galaxy uncovers the earliest metals known to date up to $z=9.1096\pm0.0006$ by detecting the bright [OIII] 88~$μ$m nebular line, indicating the onset of star formation 250 million years after the Big Bang, i.e., corresponding to a redshift of $z\sim15$. These latest findings lead us to a number of key questions: How and when metal enrichment happened in the EoR? What was the nature of the earliest-epoch star-forming galaxies at $z=10-15$? What was the spatial distribution of such galaxies, and what was the relation to the putative large-scale ionization bubbles during the EoR? What were the dark-halo masses of such earliest-epoch star-forming galaxies? To address all these questions, we need to uncover a statistically large number of $z=10-15$ galaxies in the pre-reionization era. Here we argue two possible pathways: (1) a wide-area, sensitive blind spectroscopic survey of [OIII] 88 $μ$m line-emitting galaxies at submillimeter wavelengths, and (2) an ultra-wide-area, high-cadence photometric survey of transient sources at radio-to-(sub)millimeter wavelengths, together with the immediate follow-up spectroscopy with an ultra-wide-band spectrograph, to catch the pop-III $γ$-ray bursts.

astro-ph.GA↗

arXiv2019

Testing Star Formation Laws on Spatially Resolved Regions in a $z \approx 4.3$ Starburst Galaxy

We probe the star formation properties of the gas in AzTEC-1 in the COSMOS field, one of the best resolved and brightest starburst galaxies at $z \approx 4.3$, forming stars at a rate > 1000 $\mathrm{M_{\odot}}\,\mathrm{yr^{-1}}$. Using recent ALMA observations, we study star formation in the galaxy nucleus and an off-center star-forming clump and measure a median star formation rate (SFR) surface density of $Σ^{\mathrm{nucleus}}_{\mathrm{SFR}} = 270\pm54$ and $Σ^{\mathrm{sfclump}}_{\mathrm{SFR}} = 170\pm38\,\mathrm{M_{\odot}}\,\mathrm{yr}^{-1}\,\mathrm{kpc}^{-2}$, respectively. Following the analysis by Sharda et al. (2018), we estimate the molecular gas mass, freefall time and turbulent Mach number in these regions to predict $Σ_{\mathrm{SFR}}$ from three star formation relations in the literature. The Kennicutt-Schmidt (Kennicutt 1998, KS) relation, which is based on the gas surface density, underestimates the $Σ_{\mathrm{SFR}}$ in these regions by a factor 2-3. The $Σ_{\mathrm{SFR}}$ we calculate from the single-freefall model of Krumholz et al. 2012 (KDM) is consistent with the measured $Σ_{\mathrm{SFR}}$ in the nucleus and the star-forming clump within the uncertainties. The turbulence-regulated star formation relation by Salim et al. 2015 (SFK) agrees slightly better with the observations than the KDM relation. Our analysis reveals that an interplay between turbulence and gravity can help sustain high SFRs in high-redshift starbursts. It can also be extended to other high- and low-redshift galaxies thanks to the high angular resolution and sensitivity of ALMA observations.

astro-ph.GA↗

arXiv2019

Nature of Faint Radio Sources in GOODS-North and GOODS-South Fields - I. Spectral Index and Radio-FIR Correlation

We present the first results from the deep and wide 5 GHz radio observations of the Great Observatories Origins Deep Survey (GOODS)-North ($σ=3.5 \; μJy \; beam^{-1}$, synthesized beam size $θ=$ 1.47 arcsec $\times$ 1.42 arcsec, and 52 sources over 109 arcmin$^{2}$) and GOODS-South ($σ=3.0 \; μJy \; beam^{-1}$, $θ=$0.98 arcsec $\times$ 0.45 arcsec, and 88 sources over 190 arcmin$^{2}$) fields using the Karl G. Jansky Very Large Array. We derive radio spectral indices α between 1.4 and 5 GHz using the beam-matched images and show that the overall spectral index distribution is broad even when the measured noise and flux bias are considered. We also find a clustering of faint radio sources around $α=0.8$, but only within $S_{5GHz} < 150 \; μJy$. We demonstrate that the correct radio spectral index is important for deriving accurate rest frame radio power and analyzing the radio-FIR correlation, and adopting a single value of $α=0.8$ leads to a significant scatter and a strong bias in the analysis of the radio-FIR correlation, resulting from the broad and asymmetric spectral index distribution. When characterized by specific star formation rates, the starburst population (58%) dominates the 5 GHz radio source population, and the quiescent galaxy population (30%) follows a distinct trend in spectral index distribution and the radio-FIR correlation. Lastly, we offer suggestions on sensitivity and angular resolution for future ultra-deep surveys designed to trace the cosmic history of star formation and AGN activity using radio continuum as a probe.

astro-ph.GA↗