Rm mJy Research Articles

H i galaxy signatures in the SARAO MeerKAT galactic plane survey − III. Unveiling the obscured part of the Vela Supercluster

ABSTRACT We conducted a search for $\textrm {H}\, \scriptstyle \mathrm{I}$ emission of the gas-rich galaxies in the Vela region (260° ≤ ℓ ≤ 290°, −2° ≤ b ≤ 1°) to explore the Vela Supercluster (VSCL) at Vhel ∼ 18 000 $\rm km\, s^{-1}$, largely obscured by Galactic dust. Within the mostly Radio Frequency Interference-free band (250 < Vhel < 25 000 $\rm km\, s^{-1}$) of MeerKAT, the analysis focuses on 157 hexagonally distributed pointings extracted from the South African Radio Astronomy Observatory MeerKAT Galactic Plane Survey located in the Vela region (Vela−SMGPS). These were combined into 10 contiguous mosaics, covering an ∼90 square degrees area. Among the 843 $\textrm {H}\, \scriptstyle \mathrm{I}$ detected sources, 39 were previously discovered in the H i Parkes Zone of Avoidance survey (Vhel < 12 000 $\rm km\, s^{-1}$; rms ∼ 6 $\rm mJy\, beam^{-1}$). With the improved rms level of the Vela−SMGPS, i.e. 0.29–0.56 $\rm mJy\, beam^{-1}$, our study unveils nearly 12 times more detections (471 candidates) in that same velocity range. We furthermore could identify 187 galaxy candidates with an $\textrm {H}\, \scriptstyle \mathrm{I}$ mass limit reaching $\log (M_{\rm HI}/\rm {\rm M}_{\odot }) = 9.44$ in the VSCL velocity range Vhel ∼ 19 500 ± 3500 $\rm km\, s^{-1}$. We find indications of two wall-like overdensities that confirm the original suspicion that these walls intersect at low latitudes around longitudes of ℓ ∼ 272°–278°. We also find a strong signature most likely associated with the Hydra/Antlia extension and evidence of a previously unknown narrow filament at Vhel ∼ 12 000 $\rm km\, s^{-1}$. This paper demonstrates the efficiency of systematic $\textrm {H}\, \scriptstyle \mathrm{I}$ surveys with the Square Kilometre Array (SKA) precursor MeerKAT, even in the most obscured part of the Zone of Avoidance.

The SCUBA-2 Large eXtragalactic Survey: 850μm map, catalogue and the bright-end number counts of theXMM-LSS field

ABSTRACTWe present $850\, \mu {\rm m}$ imaging of the XMM-LSS field observed for 170 h as part of the James Clerk Maxwell Telescope SCUBA-2 Large eXtragalactic Survey (S2LXS). S2LXS XMM-LSS maps an area of $9\, {\rm deg}^2$, reaching a moderate depth of $1\sigma \simeq 4\, {\rm mJy\, beam^{-1}}$. This is the largest contiguous area of extragalactic sky mapped by James Clerk Maxwell Telescope (JCMT) at $850\, \mu {\rm m}$ to date. The wide area of the S2LXS XMM-LSS survey allows us to probe the ultra-bright ($S_{\rm 850\mu m}\gtrsim 15\, {\rm mJy}$), yet rare submillimetre population. We present the S2LXS XMM-LSS catalogue, which comprises 40 sources detected at >5σ significance, with deboosted flux densities in the range of $7$–$48\, {\rm mJy}$. We robustly measure the bright-end of the $850\, \mu {\rm m}$ number counts at flux densities ${\gt }7\, {\rm mJy}$, reducing the Poisson errors compared to existing measurements. The S2LXS XMM-LSS observed number counts show the characteristic upturn at bright fluxes, expected to be motivated by local sources of submillimetre emission and high-redshift strongly lensed galaxies. We find that the observed $850\, \mu {\rm m}$ number counts are best reproduced by model predictions that include either strong lensing or source blending from a 15-arcsec beam, indicating that both may make an important contribution to the observed overabundance of bright single dish $850\, \mu {\rm m}$ selected sources. We make the S2LXS XMM-LSS $850\, \mu {\rm m}$ map and >5σ catalogue presented here publicly available.

The SCUBA-2 Cosmology Legacy Survey: the EGS deep field – III. The evolution of faint submillimetre galaxies atz< 4

ABSTRACTWe present a demographic analysis of the physical and morphological properties of $450/850~\mu \rm m$-selected galaxies from the deep observations of the SCUBA-2 Cosmology Legacy Survey in the Extended Groth Strip that are detected below the classical submillimetre-galaxy regime ($S_{850\, \mu \rm m}\lesssim 6~\rm mJy$ beam−1) and compare them with a sample of optically selected star-forming galaxies detected in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey in the same field. We derive the evolution of the main sequence of star-forming galaxies, finding a steeper specific star formation rate versus stellar mass at z > 2.5 than previous studies. Most faint submillimetre-galaxies fall within 3σ of the main sequence, but 40 per cent are classified as starbursts. Faint submillimetre galaxies have 50 per cent larger sizes at 2 < z < 3 than optically selected star-forming galaxies of the same mass range. This is also the redshift bin where we find the largest fraction of starbursts, and hence we could be witnessing merging processes, as confirmed by the preference for visual-morphology classifications of these systems as irregular disc galaxies and mergers. Both populations show an increment towards lower redshifts (z < 2) of their concentration in H-band morphology, but faint submillimetre galaxies on average show larger concentration values at later times. These findings support the claim that faint submillimetre galaxies are mostly a population of massive dust-obscured disc-like galaxies that develop larger bulge components at later epochs. While the similarities are great, the median sizes, starburst numbers, and H-band concentration of faint submillimetre galaxies differ from those of optically selected star-forming galaxies of the same stellar mass.

LOFAR detection of a low-power radio halo in the galaxy cluster Abell 990

ABSTRACT Radio haloes are extended (∼Mpc), steep spectrum sources found in the central region of dynamically disturbed clusters of galaxies. Only a handful of radio haloes have been reported to reside in galaxy clusters with a mass $M_{500}\lesssim 5\times 10^{14}\, \mathrm{ M}_\odot$. In this paper, we present a LOw Frequency ARray (LOFAR) 144 MHz detection of a radio halo in the galaxy cluster Abell 990 with a mass of $M_{500}=(4.9\pm 0.3)\times 10^{14}\, \mathrm{ M}_\odot$. The halo has a projected size of ${\sim} 700\, {\rm kpc}$ and a flux density of $20.2\pm 2.2\, {\rm mJy}$ or a radio power of $1.2\pm 0.1\times 10^{24}\, {\rm W\, Hz}^{-1}$ at the cluster redshift (z = 0.144) that makes it one of the two haloes with the lowest radio power detected to date. Our analysis of the emission from the cluster with Chandra archival data using dynamical indicators shows that the cluster is not undergoing a major merger but is a slightly disturbed system with a mean temperature of $5\, {\rm keV}$. The low X-ray luminosity of $L_{\mathrm{ X}}=(3.66\pm 0.08)\times 10^{44}\, {\rm erg\, s}^{-1}$ in the 0.1–2.4 keV band implies that the cluster is one of the least luminous systems known to host a radio halo. Our detection of the radio halo in Abell 990 opens the possibility of detecting many more haloes in poorly explored less massive clusters with low-frequency telescopes such as LOFAR, Murchison Widefield Array (MWA, Phase II), and upgraded Giant Metrewave Radio Telescope (uGMRT).

NEPSC2, the North Ecliptic Pole SCUBA-2 survey: 850-μm map and catalogue of 850-μm-selected sources over 2 deg2

ABSTRACT We present an 850-μm mosaic map and extracted catalogue of submillimetre sources in the extended North Ecliptic Pole (NEP) region over about 2 deg2. The 850-μm map is constructed using newly obtained observations by SCUBA-2 at the East Asian Observatory’s James Clerk Maxwell Telescope, carried out using the observatory’s large programme opportunities. The recent 850-μm survey has extended the submillimetre data coverage by almost a factor of 4 compared to previous surveys, with a depth of $\sigma _\text{rms}\, {=}\, 1.0$–$2.3\, {\rm mJy}\, {\rm beam}^{-1}$. The catalogue contains 549 sources selected above a significance level of 4σ, where the false-detection rate is 10 per cent; a higher threshold of 4.5σ is required in order to achieve a false-detection rate below 3 per cent, which results in 342 sources being selected. Despite the large spatial variation of the noise, the deboosted flux density of sources is comparable to results from the SCUBA-2 Cosmology Legacy Survey, which covered the central 0.6 deg2 of our survey area with better sensitivity. We construct the source counts at 850 μm, finding results in agreement with other 850-μm surveys in cosmological blank fields over S850 = 4–15 mJy. We find a slight excess of bright galaxies ($S_{850}\, {\gt }\, 15$ mJy), which can be considered to be at $z_\text{phot}\, {=}\, 2$–4. The 850-μm data add valuable long-wavelength information to mid-infrared-selected sources from the AKARI NEP-deep and NEP-wide surveys, which will be helpful in preparing for future near-infrared to millimetre wavelength observations in the NEP region. Our 850-μm mosaic map and source catalogue will be made publicly available.

Radiative properties of the first galaxies: rapid transition between UV and infrared bright phases

ABSTRACT Recent observations have successfully detected UV-bright and infrared-bright galaxies in the epoch of reionization. However, the origin of their radiative properties has not been understood yet. Combining cosmological hydrodynamic simulations and radiative transfer calculations, we present predictions of multiwavelength radiative properties of the first galaxies at z ∼ 6–15. Using zoom-in initial conditions, we investigate three massive galaxies and their satellites in different environment and halo masses at z = 6: $M_{\rm h}= 2.4\times 10^{10}\,$, $1.6\times 10^{11}\, $, and $0.7\times 10^{12}\, {\rm M_{\odot }}$. We find that most of the gas and dust are ejected from star-forming regions by supernova feedback, which allows the UV photons to escape. We show that the peak of the spectral energy distribution (SED) rapidly changes between UV and infrared wavelengths on a time-scale of ∼ 100 Myr due to intermittent star formation and feedback, and the escape fraction of UV photons fluctuates in the range of 0.2–0.8 at z < 10 with a time-averaged value of 0.3. When dusty gas covers the star-forming regions, the galaxies become bright in the observed-frame sub-millimeter wavelengths. We predict the detectability of high-z galaxies with the Atacama Large Millimeter Array (ALMA). For a sensitivity limit of $0.1\, {\rm mJy}$ at $850\, {\rm \mu m}$, the detection probability of galaxies in haloes $M_{\rm h}\gtrsim 10^{11}\, \, {\rm M_{\odot }}$ at z ≲ 7 exceeds fifty per cent. We argue that supernova feedback can produce the observed diversity of SEDs for high-z galaxies.

ALMACAL II: Extreme Star Formation Rate Densities in Dusty Starbursts Revealed by ALMA 20 mas Resolution Imaging

Abstract We present ultrahigh spatial resolution (∼20 mas or 150 pc) ALMA observations of the dust continuum at 920 μm and 1.2 mm in two submillimeter sources at z = 3.442, ALMACAL–1 (A–1: ) and ALMACAL–2 (A–2: ). About half of the star formation in each of these sources is dominated by a single compact clump (FWHM size of ∼350 pc). In A–1, two additional fainter clumps are found. The star formation rate (SFR) surface densities of all these clumps are extremely high, to , the highest rates found in high-redshift galaxies. Given their geometry and identical redshifts, there is a possibility that A–1 and A–2 are the lensed images of a single background source that are gravitationally amplified by the blazar host. If this were the case, the effective radius of the dusty galaxy in the source plane would be and the demagnified SFR surface density would be ∼ 10,000 , comparable with the eastern nucleus of Arp 220. Although we cannot rule out an AGN contribution, our results suggest that a significant percentage of the enormous far-IR luminosity in some dusty starbursts is extremely compact. The high in these sources could only be measured thanks to the ultrahigh-resolution ALMA observations used in this work, demonstrating that long-baseline observations are essential to study and interpret the properties of dusty starbursts in the early Universe.

GMRT 610-MHz observations of the faint radio source population – and what these tell us about the higher radio-frequency sky

We present 610-MHz Giant Metrewave Radio Telescope observations of 0.84 deg$^2$ of the AMI001 field (centred on $00^{\rm h} 23^{\rm m} 10^{\rm s}$, $+31^{\circ} 53'$) with an r.m.s. noise of 18 $\mu$Jy beam$^{-1}$ in the centre of the field. 955 sources are detected, and 814 are included in the source count analysis. The source counts from these observations are consistent with previous work. We have used these data to study the spectral index distribution of a sample of sources selected at 15.7 GHz from the recent deep extension to the Tenth Cambridge (10C) survey. The median spectral index, $\alpha$, (where $S \propto \nu^{-\alpha}$) between $0.08 < S_{15.7~\rm GHz} / \rm mJy < 0.2$ is $0.32 \pm 0.14$, showing that star-forming galaxies, which have much steeper spectra, are not contributing significantly to this population. This is in contrast to several models, but in agreement with the results from the 10C ultra-deep source counts; the high-frequency sky therefore continues to be dominated by radio galaxies down to $S_{15.7~\rm GHz} = 0.1$ mJy.

PROTOPLANETARY DISKS INCLUDING RADIATIVE FEEDBACK FROM ACCRETING PLANETS

While recent observational progress is converging on the detection of compact regions of thermal emission due to embedded protoplanets, further theoretical predictions are needed to understand the response of a protoplanetary disk to the planet formation radiative feedback. This is particularly important to make predictions for the observability of circumplanetary regions. In this work we use 2D hydrodynamical simulations to examine the evolution of a viscous protoplanetary disk in which a luminous Jupiter-mass planet is embedded. We use an energy equation which includes the radiative heating of the planet as an additional mechanism for planet formation feedback. Several models are computed for planet luminosities ranging from $10^{-5}$ to $10^{-3}$ Solar luminosities. We find that the planet radiative feedback enhances the disk's accretion rate at the planet's orbital radius, producing a hotter and more luminous environement around the planet, independently of the prescription used to model the disk's turbulent viscosity. We also estimate the thermal signature of the planet feedback for our range of planet luminosities, finding that the emitted spectrum of a purely active disk, without passive heating, is appreciably modified in the infrared. We simulate the protoplanetary disk around HD 100546 where a planet companion is located at about 68 au from the star. Assuming the planet mass is 5 Jupiter masses and its luminosity is $\sim 2.5 \times 10^{-4} \, L_\odot$, we find that the radiative feedback of the planet increases the luminosity of its $\sim 5$ au circumplanetary disk from $10^{-5} \, \rm L_\odot$ (without feedback) to $10^{-3} \, \rm L_\odot$, corresponding to an emission of $\sim 1 \, \rm mJy$ in $L^\prime$ band after radiative transfer calculations, a value that is in good agreement with HD 100546b observations.

Polarized light from Sagittarius A* in the near-infraredKs-band

We present a statistical analysis of polarized near-infrared (NIR) light from Sgr A*, the radio source associated with the supermassive black hole at the center of the Milky Way. The observations have been carried out using the adaptive optics instrument NACO at the VLT UT4 in the infrared $K_\mathrm{s}$-band from 2004 to 2012. Several polarized flux excursions were observed during these years. Linear polarization at 2.2 $\mu m$, its statistics and time variation, can be used constrain the physical conditions of the accretion process onto this supermassive black hole. With an exponent of about 4 for the number density histogram of fluxes above 5~mJy, the distribution of polarized flux density is closely linked to the single state power-law distribution of the total $K_\mathrm{s}$-band flux densities reported earlier. We find typical polarization degrees of the order of 20\%$\pm$10\% and a preferred polarization angle of 13$^o$$\pm$15$^o$. Simulations show the uncertainties under a total flux density of $\sim 2\,{\rm mJy}$ are probably dominated by observational effects. At higher flux densities there are intrinsic variations of polarization degree and angle within rather well constrained ranges. Since the emission is most likely due to optically thin synchrotron radiation, this preferred polarization angle we find is very likely coupled to the intrinsic orientation of the Sgr A* system i.e. a disk or jet/wind scenario associated with the super massive black hole. If they are indeed linked to structural features of the source the data imply a rather stable geometry and accretion process for the Sgr A* system.

PHOTOMETRIC REDSHIFTS OF SUBMILLIMETER GALAXIES

We use the photometric redshift method of Chakrabarti & McKee (2008) to infer photometric redshifts of submillimeter galaxies with far-IR (FIR) $\it{Herschel}$ data obtained as part of the PACS Evolutionary Probe (PEP) program. For the sample with spectroscopic redshifts, we demonstrate the validity of this method over a large range of redshifts ($ 4 \ga z \ga 0.3$) and luminosities, finding an average accuracy in $(1+z_{\rm phot})/(1+z_{\rm spec})$ of 10%. Thus, this method is more accurate than other FIR photometric redshift methods. This method is different from typical FIR photometric methods in deriving redshifts from the light-to-gas mass ($L/M$) ratio of infrared-bright galaxies inferred from the FIR spectral energy distribution (SED), rather than dust temperatures. Once the redshift is derived, we can determine physical properties of infrared bright galaxies, including the temperature variation within the dust envelope, luminosity, mass, and surface density. We use data from the GOODS-S field to calculate the star formation rate density (SFRD) of sub-mm bright sources detected by AzTEC and PACS. The AzTEC-PACS sources, which have a threshold $850 \micron$ flux $\ga 5 \rm mJy$, contribute 15% of the SFRD from all ULIRGs ($L_{\rm IR} \ga 10^{12} L_{\odot}$), and 3% of the total SFRD at $z \sim 2$.