We present a model that elucidates why gas depletion times in galaxies are long compared to the time scales of the processes driving the evolution of the interstellar medium. We show that global depletion times are not set by any "bottleneck" in the process of gas evolution towards the star-forming state. Instead, depletion times are long because star-forming gas converts only a small fraction of its mass into stars before it is dispersed by dynamical and feedback processes. Thus, complete depletion requires that gas transitions between star-forming and non-star-forming states multiple times. Our model does not rely on the assumption of equilibrium and can be used to interpret trends of depletion times with the properties of observed galaxies and the parameters of star formation and feedback recipes in galaxy simulations. In particular, the model explains the mechanism by which feedback self-regulates star formation rate in simulations and makes it insensitive to the local star formation efficiency. We illustrate our model using the results of an isolated $L_*$-sized disk galaxy simulation that reproduces the observed Kennicutt-Schmidt relation for both molecular and atomic gas. Interestingly, the relation for molecular gas is close to linear on kiloparsec scales, even though a non-linear relation is adopted in simulation cells. This difference is due to stellar feedback, which breaks the self-similar scaling of the gas density PDF with the average gas surface density.
$\rm Context$: Star clusters interact with the ISM in various ways, most
importantly in the destruction of molecular star-forming clouds, resulting in
inefficient star formation on galactic scales. On cloud scales, ionizing
radiation creates \hii regions, while stellar winds and supernovae drive the
ISM into thin shells. These shells are accelerated by the combined effect of
winds, radiation pressure and supernova explosions, and slowed down by gravity.
Since radiative and mechanical feedback is highly interconnected, they must be
taken into account in a self-consistent and combined manner, including the
coupling of radiation and matter.
$\rm Aim$: We seek to identify the efficiency with which different stellar
feedback mechanisms couple to the dynamical evolution of isolated massive
clouds ($\geq 10^5\,M_{\odot}$) and self-consistently solve for the dynamical
expansion resulting from feedback.
$\rm Methods$: We present a new semi-analytic one-dimensional feedback model
to calculate shell dynamics and structure simultaneously. It allows us to scan
a large range of physical parameters and to estimate escape fractions of
ionizing radiation $f_{\rm{esc,i}}$, the minimum star formation efficiency
$\epsilon_{\rm{min}}$ required to drive an outflow, and recollapse time scales
for clouds that are not destroyed by feedback.
$\rm Results$: We find that there is no simple answer to the question of what
dominates cloud dynamics, and that each feedback process significantly
influences the efficiency of the others. We show that variations in natal cloud
density can very easily explain differences between dense-bound and
diffuse-open star clusters. We also predict a 4-6 Myr age difference for
massive clusters with multiple generations as a consequence of feedback.
Using the latest cosmological hydrodynamic N-body simulations of groups and clusters, we study how location in phase-space coordinates at $z$$=$$0$ can provide information on environmental effects acting in clusters. We confirm the results of previous authors showing that galaxies tend to follow a typical path in phase-space as they settle into the cluster potential. As such, different regions of phase-space can be associated with different times since first infalling into the cluster. However, in addition, we see a clear trend between total mass loss due to cluster tides, and time since infall. Thus we find location in phase-space provides information on both infall time, and tidal mass loss. We find the predictive power of phase-space diagrams remains even when projected quantities are used (i.e. line-of-sight velocities, and projected distances from the cluster). We provide figures that can be directly compared with observed samples of cluster galaxies and we also provide the data used to make them as supplementary data, in order to encourage the use of phase-space diagrams as a tool to understand cluster environmental effects. We find that our results depend very weakly on galaxy mass or host mass, so the predictions in our phase-space diagrams can be applied to groups or clusters alike, or to galaxy populations from dwarfs up to giants.
We present a comprehensive analysis of the spin temperature/covering factor degeneracy, T/f, in damped Lyman-alpha absorption systems. By normalising the upper limits and including these via a survival analysis, there is, as previously claimed, an apparent increase in T/f with redshift at z > 1. However, when we account for the geometry effects of an expanding Universe, neglected by the previous studies, this increase in T/f at z > 1 is preceded by a decrease at z < 1. Using high resolution radio images of the background continuum sources, we can transform the T/f degeneracy to T/d^2, where d is the projected linear size of the absorber. Again, there is no overall increase with redshift, although a dip at z ~ 2 persists. Furthermore, we find d^2/T to follow a similar variation with redshift as the star formation rate. This suggests that, although the total hydrogen column density shows little relation to the SFR, the fraction of the cold neutral medium may. Therefore, further efforts to link the neutral gas with the star formation history should also consider the cool component of the gas.
Neutral hydrogen clouds are known to exist in the Universe, however their spatial distributions and physical properties are poorly understood. Such missing information can be studied by the new generation Chinese radio telescopes through a blind searching of 21-cm absorption systems. We forecast the capabilities of surveys of 21-cm absorption systems by two representative radio telescopes in China -- Five-hundred-meter Aperture Spherical radio Telescope (FAST) and Tianlai 21-cm cosmology experiment (Tianlai). Facilitated by either the high sensitivity (FAST) or the wide field of view (Tianlai) of these telescopes, more than a thousand 21-cm absorption systems can be discovered in a few years, representing orders of magnitude improvement over the cumulative discoveries in the past half a century.
We present results from our Giant Metrewave Radio Telescope (GMRT) HI observations of the Arp 305 system. The system consists of two interacting spiral galaxies NGC 4016 and NGC 4017, a large amount of resultant tidal debris and a prominent tidal dwarf galaxy (TDG) candidate projected within the tidal bridge between the two principal galaxies. Our higher resolution GMRT HI mapping, compared to previous observations, allowed detailed study of smaller scale features. Our HI analysis supports the conclusion in Hancock et al. (2009) that the most recent encounter between the pair occurred $\sim$ 4 $\times$ 10$^8$ yrs ago. The GMRT observations also show HI features near NGC 4017 which may be remnants of an earlier encounter between the two galaxies. The HI properties of the Bridge TDG candidate include: M(HI) $\sim$ 6.6 $\times$ 10$^8$ msolar and V(HI) = 3500$\pm$ 7 km/s, which is in good agreement with the velocities of the parent galaxies. Additionally the TDG's HI linewidth of 30 km/s and a modest velocity gradient together with its SFR of 0.2 msolar/yr add to the evidence favouring the bridge candidate being a genuine TDG. The Bridge TDG's \textit{Spitzer} 3.6 $\mu$m and 4.5 $\mu$m counterparts with a [3.6]--[4.5] colour $\sim$ -0.2 mag suggests stellar debris may have seeded its formation. Future spectroscopic observations could confirm this formation scenario and provide the metallicity which is a key criteria for the validation for TDG candidates.
The hidden broad-line regions (BLRs) in Seyfert 2 galaxies, which display broad-emission lines (BELs) in their polarized spectra, are a key piece of evidence in support of the unified model for active galactic nuclei (AGNs). However, the detailed kinematics and geometry of hidden BLRs are still not fully understood. The virial factor obtained from reverberation mapping of type 1 AGNs may be a useful diagnostic of the nature of hidden BLRs in type 2 objects. In order to understand the hidden BLRs, we compile six type 2 objects from the literature with polarized BELs and dynamical measurements of black hole masses. All of them contain pseudobulges. We estimate their virial factors, and find the average value is 0.60 and the standard deviation is 0.69, which agree well with the value of type 1 AGNs with pseudobulges. This study demonstrates that (1) the geometry and kinematics of BLR are similar in type 1 and type 2 AGNs of the same bulge type (pseudobulges), and (2) the small values of virial factors in Seyfert 2 galaxies suggest that, similar to type 1 AGNs, BLRs tend to be very thick disks in type 2 objects.
We present stellar density maps of the Galactic outer disc with red clump stars from the LAMOST data. These samples are separated into younger (mean age ~ 2.7 Gyr) and older (mean age ~ 4.6 Gyr) populations so that they can trace the variation of the structures with ages in the range of the Galactocentric radius R from 9 to 13.5 kpc. We show that both the scale heights for the two populations increase with R and display radial gradients of 48 +/- 6 and 40 +/- 4 pc/kpc for the older and younger populations, respectively. This is evident that the flaring occurs in the thin disc populations with a wide range of ages. Moreover, the intensity of flaring seems not significantly related to the age of the thin disc populations. On the other hand, the scale lengths of the radial surface density profiles are 4.7 +/- 0.5 kpc for the younger and 3.4 +/- 0.2 kpc for the older population, meaning that the younger disc population is more radially extended than the older one. Although the fraction of the younger population mildly increases from 28% at R ~ 9 to about 35% at R ~ 13 kpc, the older population is prominent with the fraction no less than 65% in the outer disc.
Aims. ESO 243-49 HLX-1, otherwise known as HLX-1, is an intermediate mass black hole (IMBH) candidate located 8" (3.7 Kpc) from the centre of the edge-on S0 galaxy ESO 243-49. How the black hole came to be associated with this galaxy, and the nature of the environment in which it resides, are still unclear. Using multi-wavelength observations we investigate the nature of the medium surrounding HLX-1, search for evidence of past mergers with ESO 243-49 and constrain parameters of the galaxy. Methods. We reduce and analyse integral field unit observations of ESO 243-49 that were taken with the MUSE instrument on the VLT. Using complementary multi-wavelength data, including X-Shooter, HST, Swift, Chandra and ATCA data, we further examine the vicinity of HLX-1. We additionally examine the nature of the host galaxy and estimate the mass of the central supermassive black hole (SMBH) in ESO 243-49. Results. No evidence for a recent minor-merger that could result in the presence of the IMBH is discerned, but the data are compatible with a scenario in which minor mergers may have occurred in the history of ESO 243-49. The MUSE data reveal a rapidly rotating disc in the centre of the galaxy, around the SMBH. The mass of the SMBH at the centre of ESO 243-49 is estimated to be 0.5-23 $\times$ 10$^7$ M$_\odot$. Studying the spectra of HLX-1, that were taken in the low/hard state, we determine H$_\alpha$ flux variability to be at least a factor 6, compared to observations taken during the high/soft state. This H$_\alpha$ flux variability over one year indicates that the line originates close to the IMBH, excluding the possibility that the line emanates from a surrounding nebula or a star cluster. The large variability associated with the X-ray states of HLX-1 confirms that the H$_\alpha$ line is associated with the object and therefore validates the distance to HLX-1.
Galaxy groups and clusters are the main tools used to test cosmological
models and to study the environmental effect of galaxy formation. This work
provides a catalogue of galaxy groups and clusters, as well as potentially
merging systems based on the SDSS main galaxy survey. We identified galaxy
groups and clusters using the modified friends-of-friends (FoF) group finder
designed specifically for flux-limited galaxy surveys. The FoF group membership
is refined by multimodality analysis to find subgroups and by using the group
virial radius and escape velocity to expose unbound galaxies. We look for
merging systems by comparing distances between group centres with group radii.
The analysis results in a catalogue of 88662 galaxy groups with at least two
members. Among them are 6873 systems with at least six members which we
consider to be more reliable groups. We find 498 group mergers with up to six
groups. We performed a brief comparison with some known clusters in the nearby
Universe, including the Coma cluster and Abell 1750. The Coma cluster in our
catalogue is a merging system with six distinguishable subcomponents. In the
case of Abell 1750 we find a clear sign of filamentary infall toward this
cluster. Our analysis of mass-to-light ratio (M/L) of galaxy groups reveals
that M/L slightly increases with group richness.
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The Milky Way dark matter halo is formed from the accretion of smaller subhalos. These sub-units also harbor stars--typically old and metal-poor--that are deposited in the Galactic inner regions by disruption events. In this Letter, we show that the dark matter and metal-poor stars in the Solar neighborhood share similar kinematics due to their common origin. Using the high-resolution Eris simulation, which traces the evolution of both the dark matter and baryons in a realistic Milky Way analog galaxy, we demonstrate that metal-poor stars are indeed effective tracers for the local, virialized dark matter velocity distribution. The dark matter velocities in the Solar neighborhood can therefore be inferred from observations of the smooth inner halo made by the Sloan Digital Sky Survey. This empirical distribution has a lower peak speed and smaller dispersion than what is typically assumed in the Standard Halo Model, affecting the interpretation of direct detection experiments. Specifically, the bounds on the spin-independent scattering cross section are weakened by nearly an order of magnitude for masses below ~10 GeV. Upcoming data from Gaia will allow us to further refine the expected distribution for the smooth dark matter component, and to test for the presence of local substructure.
We investigate the relation between star formation rate (SFR) and stellar mass ($M_*$) in sub-galactic ($\sim 1$kpc) scale of 93 local ($0.01<z<0.02$) massive ($M_*>10^{10.5}M_{\odot}$) spiral galaxies. To derive spatially-resolved SFR and stellar mass, we perform so-called pixel-to-pixel SED fitting, which fits an observed spatially-resolved multiband SED with a library of model SEDs using Bayesian statistics approach. We use 2 bands (FUV and NUV) and 5 bands ($u$, $g$, $r$, $i$, and $z$) imaging data from Galaxy Evolution Explorer (GALEX) and Sloan Digital Sky Survey (SDSS), respectively. We find a tight nearly linear relation between the local surface density of SFR ($\Sigma_{\rm{SFR}}$) and stellar mass ($\Sigma_{*}$) which has flattening in high $\Sigma_{*}$. The near linear relation between $\Sigma_{*}$ and $\Sigma_{\rm SFR}$ suggests constant sSFR throughout the galaxies, and the scatter of the relation is directly related to that of sSFR. Therefore, we analyse the variation of sSFR in various scales. More massive galaxies on average have lower sSFR throughout them than less massive galaxies. We also find that barred galaxies have lower sSFR in a core region than non-barred galaxies. However, in the outside region, sSFR of barred and non-barred galaxies are similar and lead to the similar total sSFR.
We report on a systematic search for oxygen-bearing Complex Organic Molecules (COMs) in the Solar-like protostellar shock region L1157-B1, as part of the IRAM Large Program "Astrochemical Surveys At IRAM" (ASAI). Several COMs are unambiguously detected, some for the first time, such as ketene H$_2$CCO, dimethyl ether (CH$_3$OCH$_3$) and glycolaldehyde (HCOCH$_2$OH), and others firmly confirmed, such as formic acid (HCOOH) and ethanol (C$_2$H$_5$OH). Thanks to the high sensitivity of the observations and full coverage of the 1, 2 and 3mm wavelength bands, we detected numerous (10--125) lines from each of the detected species. Based on a simple rotational diagram analysis, we derive the excitation conditions and the column densities of the detected COMs. Combining our new results with those previously obtained towards other protostellar objects, we found a good correlation between ethanol, methanol and glycolaldehyde. We discuss the implications of these results on the possible formation routes of ethanol and glycolaldehyde.
The formation of globular clusters (GC) with their multiple stellar populations remains a puzzling, unsolved problem in astrophysics. One way to gather critical insight consists in finding sizable numbers of GC progenitors (GCP) while still near the peak of their star formation phase, at a lookback time corresponding to GC ages (~12.5 Gyr, or z ~ 5). This opportunity is quantitatively explored, calculating how many GCPs could be detected by deep imaging in the optical, near-IR and mid-IR bands. For concreteness, for the imaging camera performances those of NIRCam on board of JWST are adopted. The number of GCPs that could be detected scales linearly with their mass, i.e., on how much more massive GCPs were compared to their GC progeny, and perspectives look promising. Besides providing direct evidence on GC formation, the detection of GCPs, their clustering, with or without a central galaxy already in place, would shed light on the relative timing of GC formation and galaxy growth and assembly. All this, may be the result of dedicated observations as well as a side benefit of deep imaging meant to search for the agents of cosmic reionization.
The sample of known star clusters, the fundamental building blocks of
galaxies, in the Milky Way is still extremely incomplete for objects beyond a
distance of 1-2kpc. Many of the more distant and young clusters are compact and
hidden behind large amounts of extinction. We thus utilised the deep high
resolution near infrared surveys UGPS and VVV to uncover so far unknown compact
clusters and to analyse their properties.
Images of all objects in the area covered by these two surveys, and which are
listed as Galaxy in SIMBAD have been inspected and 125 so far unknown stellar
clusters and candidate clusters have been identified. Based on the frequent
associations with star formation indicators (nebulosities, IRAS sources, Hii
regions, masers) we find that the typical cluster in our sample is young, at
distances between 1-10kpc and has a typical apparent radius of 25arcsec. We
suggest more systematic searches e.g. at all positions of 2MASS extended
sources to increase the completeness of the known cluster sample beyond
distances of 2kpc.
We demonstrate that, for the baseline design of the CORE satellite mission, the polarized foregrounds can be controlled at the level required to allow the detection of the primordial cosmic microwave background (CMB) $B$-mode polarization with the desired accuracy at both reionization and recombination scales, for tensor-to-scalar ratio values of $r\gtrsim 5\times 10^{-3}$. Under the assumption of perfect control of lensing effects, CORE would measure an unbiased estimate of $r=5\times 10^{-3}$ with an uncertainty of ${\sigma(r=5\times 10^{-3})=0.4\times 10^{-3}}$ after foreground cleaning. In presence of both gravitational lensing effects and astrophysical foregrounds, the significance of the detection is lowered, with CORE achieving yet a $4\sigma$-measurement of $r=5\times 10^{-3}$ after foreground cleaning and $60$% delensing. We deliberately consider detailed sky simulations based on state-of-the-art CMB observations that consist of CMB polarization with $\tau=0.055$ and tensor-to-scalar values ranging from $r=10^{-2}$ to $10^{-3}$, Galactic synchrotron and thermal dust polarization with variable spectral indices over the sky, polarized anomalous microwave emission, polarized infrared and radio sources, and gravitational lensing effects. Using both parametric and blind approaches, we perform the full component separation and likelihood analysis of the simulations, allowing us to quantify both uncertainties and biases on the reconstructed primordial $B$-modes. We report two sources of potential bias for the detection of the primordial B-modes by future CMB experiments: (i) incorrect foreground models, (ii) averaging of foreground spectral indices by pixellization and beam convolution.
We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24micron data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from their location in the various color-color and color-magnitude diagrams, and the presence of Halpha emission, mid-infrared excess emission, and X-ray emission. The reddening law toward IC 1805 is nearly normal (R_V = 3.05+/-0.06). However, the distance modulus of the cluster is estimated to be 11.9+/-0.2 mag (d = 2.4+/-0.2 kpc) from the reddening-free color-magnitude diagrams, which is larger than the distance to the nearby massive star-forming region W3(OH) measured from the radio VLBA astrometry. We also determined the age of IC 1805 (tau_MSTO = 3.5 Myr). In addition, we critically compared the age and mass scale from two pre-main-sequence evolution models. The initial mass function with a Salpeter-type slope of Gamma = -1.3+/-0.2 was obtained and the total mass of IC 1805 was estimated to be about 2700+/-200 M_sun. Finally, we found our distance determination to be statistically consistent with the Tycho-Gaia Astrometric Solution Data Release 1, within the errors. The proper motion of the B-type stars shows an elongated distribution along the Galactic plane, which could be explained by some of the B-type stars being formed in small clouds dispersed by previous episodes of star formation or supernova explosions.
At early stages of stellar evolution young stars show powerful jets and/or outflows that interact with protoplanetary discs and their surroundings. Despite the scarce knowledge about the interaction of jets and/or outflows with discs, spectroscopic studies based on Herschel and ISO data suggests that gas shocked by jets and/or outflows can be traced by far-IR (FIR) emission in certain sources. We want to provide a consistent catalogue of selected atomic ([OI] and [CII]) and molecular (CO, OH, and H$_{2}$O) line fluxes observed in the FIR, separate and characterize the contribution from the jet and the disc to the observed line emission, and place the observations in an evolutionary picture. The atomic and molecular FIR (60-190 $\rm \mu m$) line emission of protoplanetary discs around 76 T Tauri stars located in Taurus are analysed. The observations were carried out within the Herschel key programme Gas in Protoplanetary Systems (GASPS). The spectra were obtained with the Photodetector Array Camera and Spectrometer (PACS). The sample is first divided in outflow and non-outflow sources according to literature tabulations. With the aid of archival stellar/disc and jet/outflow tracers and model predictions (PDRs and shocks), correlations are explored to constrain the physical mechanisms behind the observed line emission. The much higher detection rate of emission lines in outflow sources and the compatibility of line ratios with shock model predictions supports the idea of a dominant contribution from the jet/outflow to the line emission, in particular at earlier stages of the stellar evolution as the brightness of FIR lines depends in large part on the specific evolutionary stage. [Abridged Abstract]
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The absolute number and the density profiles of different types of stars in the solar neighborhood are a fundamental anchor for studies of the initial mass function, stellar evolution, and galactic structure. Using data from the Gaia DR1 Tycho-Gaia Astrometric Solution, we reconstruct Gaia's selection function and we determine Gaia's volume completeness, the local number density, and the vertical profiles of different spectral types along the main sequence from early A stars to late K stars as well as along the giant branch. We clearly detect the expected flattening of the stellar density profile near the mid-plane for all stellar types: All vertical profiles are well represented by sech^2 profiles, with scale heights ranging from ~50 pc for A stars to ~150 pc for G and K dwarfs and giants. We determine the luminosity function along the main sequence for M_V < 7 (M >~ $0.72 M_\odot$) and along the giant branch for M_J >~ -2.5. Converting this to a mass function, we find that the high-mass (M > $1\,M_\odot$) present-day mass function along the main sequence is d n / d M = 0.016 $(M/M_\odot)^{-4.7}$ stars/pc^3/$M_\odot$. Extrapolating below M = $0.72\,M_\odot$, we find a total mid-plane stellar density of 0.040+/-0.002 $M_\odot$/pc^3. Giants contribute 0.00039+/-0.00001 stars/pc^3 or about 0.00046+/-0.00005 $M_\odot$/pc^3. The star-formation rate surface density is \Sigma(t) = 7+/-1 exp(-t/[7+/-1 Gyr]) $M_\odot$/pc^2/Gyr. Surprisingly, we find that the Sun is exactly at the mid-plane defined by A and F stars (zsun = -0.9+/-0.9 pc), but appears to be offset from the mid-plane defined by older stars (zsun = 29+/-4 pc with respect to giants). Overall, we find that Gaia DR1's selection biases are manageable and allow a detailed new inventory of the solar neighborhood to be made that agrees with and extends previous studies. This bodes well for mapping the Milky Way with the full Gaia data set.
GASP (GAs Stripping Phenomena in galaxies with MUSE) is a new integral-field spectroscopic survey with MUSE at the VLT aiming at studying gas removal processes in galaxies. We present an overview of the survey and show a first example of a galaxy undergoing strong gas stripping. GASP is obtaining deep MUSE data for 114 galaxies at z=0.04-0.07 with stellar masses in the range 10^9.2-10^11.5 M_sun in different environments (galaxy clusters and groups, over more than four orders of magnitude in halo mass). GASP targets galaxies with optical signatures of unilateral debris or tails reminiscent of gas stripping processes ("jellyfish galaxies"), as well as a control sample of disk galaxies with no morphological anomalies. GASP is the only existing Integral Field Unit (IFU) survey covering both the main galaxy body and the outskirts and surroundings, where the IFU data can reveal the presence and the origin of the outer gas. To demonstrate GASP's ability to probe the physics of gas and stars, we show the complete analysis of a textbook case of a "jellyfish" galaxy, JO206. This is a massive galaxy (9 x 10^10 M_sun in a low-mass cluster (sigma ~500 km/s), at a small projected clustercentric radius and a high relative velocity, with >=90kpc-long tentacles of ionized gas stripped away by ram pressure. We present the spatially resolved kinematics and physical properties of gas and stars, and depict the evolutionary history of this galaxy.
This paper presents a spatially-resolved kinematic study of the jellyfish galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS) in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studying the environment of JO201, we find that it is moving through the dense intra-cluster medium of Abell 85 at supersonic speeds along our line of sight, and that it is likely accompanied by a small group of galaxies. Given the density of the intra-cluster medium and the galaxy's mass, projected position and velocity within the cluster, we estimate that JO201 must so far have lost ~50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth stellar disk, accompanied by large projected tails of ionised (Halpha) gas, composed of kinematically cold (velocity dispersion <40km/s) star-forming knots and very warm (>100km/s) diffuse emission which extend out to at least ~50 kpc from the galaxy centre. The ionised Halpha-emitting gas in the disk rotates with the stars out to ~6 kpc but in the disk outskirts becomes increasingly redshifted with respect to the (undisturbed) stellar disk. The observed disturbances are consistent with the presence of gas trailing behind the stellar component, resulting from intense face-on RPS happening along the line of sight. Our kinematic analysis is consistent with the estimated fraction of lost gas, and reveals that stripping of the disk happens outside-in, causing shock heating and gas compression in the stripped tails.
The so-called jellyfish galaxies are objects exhibiting disturbed morphology, mostly in the form of tails of gas stripped from the main body of the galaxy. Several works have strongly suggested ram pressure stripping to be the mechanism driving this phenomenon. Here, we focus on one of these objects, drawn from a sample of optically selected jellyfish galaxies, and use it to validate sinopsis, the spectral fitting code that will be used for the analysis of the GASP (GAs Stripping Phenomena in galaxies with MUSE) survey, and study the spatial distribution and physical properties of gas and stellar populations in this galaxy. We compare the model spectra to those obtained with gandalf, a code with similar features widely used to interpret the kinematic of stars and gas in galaxies from IFU data. We find that sinopsis can reproduce the pixel-by-pixel spectra of this galaxy at least as good as gandalf does, providing reliable estimates of the underlying stellar absorption to properly correct the nebular gas emission. Using these results, we find strong evidences of a double effect of ram pressure exerted by the intracluster medium onto the gas of the galaxy. A moderate burst of star formation, dating between 20 and 500 Myr ago and involving the outer parts of the galaxy more strongly than the inner regions, was likely induced by a first interaction of the galaxy with the intracluster medium. Stripping by ram pressure, plus probable gas depletion due to star formation, contributed to create a truncated ionized gas disk. The presence of an extended stellar tail on only one side of the disk, points instead to another kind of process, likely a gravitational interaction by a fly-by or a close encounter with another galaxy in the cluster.
We study the heating mechansims and Ly{\alpha} escape fractions of 35 Ly{\alpha} blobs (LABs) at z = 3.1 in the SSA22 field, using the submillimeter (submm) data from the ALMA and the SCUBA-2 on the JCMT, and the radio data from the VLA. With ALMA and JCMT/SCUBA-2, we have identified dust continuum sources in 11 out of 35 LABs in the SSA22 field, with star formation rates (SFRs) of above 100Msun/yr. Using VLA, we have detected likely radio counterparts in 9 out of 29 LABs in the SSA22 field. We find that a radio excess in the submm/radio detected LABs is common, suggesting that active galactic nuclei (AGN) may often be present in these systems. Most radio sources without X-ray counterparts are located in the centers of the LABs. However, it is surprising that all X-ray counterparts avoid the central regions of their LABs. Possibly these X-ray sources are associated with merging systems, which re-distribute the interstellar meidium (ISM) and circumgalactic medium (CGM), leading to highly inhomogeneous gas. Alternatively, AGN and its feedback may also be responsible for inhomogeneous Ly{\alpha} morphology in these LABs. We obtain escape fractions of Ly{\alpha} photons for the LABs based on the submm and Ly{\alpha} data, and find that the Ly{\alpha} escape fractions in the LABs are significantly lower than those found for Ly{\alpha} emitters (LAEs) in other studies. We suspect that this large difference is due to the SCUBA-2 detection threshold, the high dust attenuation indicated by the large SFRs in our sample, as well as the dense large-scale environment in SSA22.
This is the first paper of a series dedicated to nebular physics and the chemical evolution of nearby galaxies by investigating large samples of HII regions with the CFHT imaging spectrograph SITELLE. We present a technique adapted to imaging spectroscopy to identify and extract parameters from 4285 HII region candidates found in the disc of NGC\,628. Using both the spatial and spectral capabilities of SITELLE, our technique enables the extraction of the position, dust extinction, velocity, H$\alpha$ profile, diffuse ionized gas (DIG) background, luminosity, size, morphological type, and the emission line fluxes for individual spaxels and the integrated spectrum for each region. We have produced a well-sampled HII region luminosity function and studied its variation with galactocentric radius and level of the DIG background. We found a slope $\alpha$ of $-$1.12$\pm$0.03 with no evidence of a break at high luminosity. Based on the width of the region profile, bright regions are rather compact, while faint regions are seen over a wide range of sizes. The radius function reveals a slope of $-$1.81$\pm$0.02. BPT diagrams of the individual spaxels and integrated line ratios confirm that most detections are HII regions. Also, maps of the line ratios show complex variations of the ionization conditions within HII regions. All this information is compiled in a new catalog for HII regions. The objective of this database is to provide a complete sample which will be used to study the whole parameter space covered by the physical conditions in active star-forming regions.
H2CO is one of the most readily detected organic molecules in protoplanetary disks. Yet its distribution and dominant formation pathway(s) remain largely unconstrained. To address these issues, we present ALMA observations of two H2CO lines (3_{12}-2_{11} and 5_{15}-4_{14}) at 0".5 (~30 au) spatial resolution toward the disk around the nearby T Tauri star TW Hya. Emission from both lines is spatially resolved, showing a central depression, a peak at 0".4 radius, and a radial decline at larger radii with a bump at ~1", near the millimeter continuum edge. We adopt a physical model for the disk and use toy models to explore the radial and vertical H2CO abundance structure. We find that the observed emission implies the presence of at least two distinct H2CO gas reservoirs: (1) a warm and unresolved inner component (<10 au), and (2) an outer component that extends from ~15 au to beyond the millimeter continuum edge. The outer component is further constrained by the line ratio to arise in a more elevated disk layer at larger radii. The inferred H2CO abundance structure agrees well with disk chemistry models, which predict efficient H2CO gas-phase formation close to the star, and cold H2CO grain surface formation, through H additions to condensed CO, followed by non-thermal desorption in the outer disk. The implied presence of active grain surface chemistry in the TW Hya disk is consistent with the recent detection of CH3OH emission, and suggests that more complex organic molecules are formed in disks, as well.
Studies of cluster galaxies are increasingly finding galaxies with spectacular one-sided tails of gas and young stars, suggestive of intense ram-pressure stripping. These so-called "jellyfish" galaxies typically have late-type morphology. In this paper, we present MUSE observations of an elliptical galaxy in Abell 2670 with long tails of material visible in the optical spectra, as well as blobs with tadpole-like morphology. The spectra in the central part of the galaxy reveals a stellar component as well as ionized gas. The stellar component does not have significant rotation, while the ionized gas defines a clear star-forming gas disk. We argue, based on deep optical images of the galaxy, that the gas was most likely acquired during a past wet merger. It is possible that the star-forming blobs are also remnants of the merger. In addition, the direction and kinematics of the one-sided ionized tails, combined with the tadpole morphology of the star-forming blobs, strongly suggests that the system is undergoing ram pressure from the intracluster medium. In summary, this paper presents the discovery of a post-merger elliptical galaxy undergoing ram pressure stripping.
The kinematic dispersions of disc stars can be used to measure the dynamic contributions of baryons to the rotation curves of spiral galaxies and hence to trace the amount and distribution of the remaining dark matter. However, the simple single-component infinite disc model traditionally used to convert stellar dispersions to mass-densities is no longer adequate. The dark matter halo has a significant effect upon the stellar dispersions for any non-maximal disc. The correction for cuspy dark matter halos is particularly large, suggesting that such models are not consistent with the observed stellar dispersions. When a more realistic model for the vertical gravity of the disc is used, the derived stellar surface densities are generally larger (smaller) for disc radii smaller (larger) than 2.3 times the radial scale-length. When the vertical gravity correction is applied to the radially resolved stellar mass-to-light ratios derived by the DiskMass consortium, the true values are not constant but decrease with radius, as expected from photometric colour gradients, and the true mass scale-lengths are about 80% of the photometric scale-lengths. The effects of a thin gaseous disc are larger than expected, especially when an allowance is made for optically thick or CO-dark gas. The presence of a thick-disc stellar component has severe consequences, particularly if its radial scale-length is smaller than that of the thin disc, as it appears to be in the Milky Way.
Studying the molecular component of the interstellar medium in metal-poor galaxies has been challenging because of the faintness of carbon monoxide emission, the most common proxy of H2. Here we present new detections of molecular gas at low metallicities, and assess the physical conditions in the gas through various CO transitions for 8 galaxies. For one, NGC 1140 (Z/Zsun ~ 0.3), two detections of 13CO isotopologues and atomic carbon, [CI](1-0), and an upper limit for HCN(1-0) are also reported. After correcting to a common beam size, we compared 12CO(2-1)/12CO(1-0) (R21) and 12CO(3-2)/12CO(1-0) (R31) line ratios of our sample with galaxies from the literature and find that only NGC 1140 shows extreme values (R21 ~ R31 ~ 2). Fitting physical models to the 12CO and 13CO emission in NGC 1140 suggests that the molecular gas is cool (kinetic temperature Tkin<=20 K), dense (H2 volume density nH2 >= $10^6$ cm$^{-3}$), with moderate CO column density (NCO ~ $10^{16}$ cm$^{-2}$) and low filling factor. Surprisingly, the [12CO]/[13CO] abundance ratio in NGC 1140 is very low (~ 8-20), lower even than the value of 24 found in the Galactic Center. The young age of the starburst in NGC 1140 precludes 13C enrichment from evolved intermediate-mass stars; instead we attribute the low ratio to charge-exchange reactions and fractionation, because of the enhanced efficiency of these processes in cool gas at moderate column densities. Fitting physical models to 12CO and [CI](1-0) emission in NGC 1140 gives an unusually low [12CO]/[12C] abundance ratio, suggesting that in this galaxy atomic carbon is at least 10 times more abundant than 12CO.
We present the first detection of the ortho-H2O 4_23-3_30 transition at 448 GHz in space. We observed this transition in the local (z = 0.010) luminous infrared (IR) galaxy ESO 320-G030 (IRAS F11506-3851) using the Atacama Large Millimeter/submillimeter Array (ALMA). The water 4_23-3_30 emission, which originates in the highly obscured nucleus of this galaxy, is spatially resolved over a region of ~65 pc in diameter and shows a regular rotation pattern compatible with the global molecular and ionized gas kinematics. The line profile is symmetric and well fitted by a Gaussian with an integrated flux of 37.0 +- 0.7 Jy km s-1 . Models predict this water transition as a potential collisionally excited maser transition. On the contrary, in this galaxy, we find that the 4_23-3_30 emission is primarily excited by the intense far-IR radiation field present in its nucleus. According to our modeling, this transition is a probe of deeply buried galaxy nuclei thanks to the high dust optical depths (tau_100{\mu}m > 1, N_H > 1e24 cm-2) required to efficiently excite it.
The diffusive shock acceleration scenario is usually invoked to explain radio relics, although the detailed driving mechanism is still a matter of debate. Our aim is to constrain models for the origin of radio relics by comparing observed relic samples with simulated ones. Here we present a framework to homogeneously extract the whole sample of known radio relics from NVSS so that it can be used for comparison with cosmological simulations. In this way, we can better handle intrinsic biases in the analysis of the radio relic population. In addition, we show some properties of the resulting NVSS sample relics such as the correlation between relic shape and orientation with respect to the cluster. Also, we briefly discuss the typical relic surface brightness and its relation to projected cluster distance and relic angular sizes.
In early 2014 the fast-moving near-infrared source G2 reached its closest approach to the supermassive black hole Sgr A* in the Galactic Center. We report on the evolution of the ionized gaseous component and the dusty component of G2 immediately after this event, revealed by new observations obtained in 2015 and 2016 with the SINFONI integral field spectrograph and the NACO imager at the ESO VLT. The spatially resolved dynamics of the Br$\gamma$ line emission can be accounted for by the ballistic motion and tidal shearing of a test-particle cloud that has followed a highly eccentric Keplerian orbit around the black hole for the last 12 years. The non-detection of a drag force or any strong hydrodynamic interaction with the hot gas in the inner accretion zone limits the ambient density to less than a few 10$^3$ cm$^{-3}$ at the distance of closest approach (1500 $R_s$), assuming G2 is a spherical cloud moving through a stationary and homogeneous atmosphere. The dust continuum emission is unresolved in L'-band, but stays consistent with the location of the Br$\gamma$ emission. The total luminosity of the Br$\gamma$ and L' emission has remained constant to within the measurement uncertainty. The nature and origin of G2 are likely related to that of the precursor source G1, since their orbital evolution is similar, though not identical. Both object are also likely related to a trailing tail structure, which is continuously connected to G2 over a large range in position and radial velocity.
Context. Methane is among the main components of the ice mantles of insterstellar dust grains, where it is at the start of a rich solid-phase chemical network. Quantification of the photon-induced desorption yield of these frozen molecules and understanding of the underlying processes is necessary to accurately model the observations and the chemical evolution of various regions of the interstellar medium. Aims. This study aims at experimentally determining absolute photodesorption yields for the CH4 molecule as a function of photon energy. The influence of the ice composition is also investigated. By studying the methane desorption from layered CH4:CO ice, indirect desorption processes triggered by the excitation of the CO molecules is monitored and quantified. Methods. Tunable monochromatic VUV light from the DESIRS beamline of the SOLEIL synchrotron is used in the 7 - 13.6 eV (177 - 91 nm) range to irradiate pure CH4 or layers of CH4 deposited on top of CO ice samples. The release of species in the gas phase is monitored by quadrupole mass spectrometry and absolute photodesorption yields of intact CH4 are deduced. Results. CH4 photodesorbs for photon energies higher than ~9.1 eV (~136 nm). The photodesorption spectrum follows the absorption spectrum of CH4, which confirms a desorption mechanism mediated by electronic transitions in the ice. When it is deposited on top of CO, CH4 desorbs between 8 and 9 eV with a pattern characteristic of CO absorption, indicating desorption induced by energy transfer from CO molecules. Conclusions. The photodesorption of CH4 from the pure ice in various interstellar environments is around 2.0 x 10^-3 molecules per incident photon. Results on CO-induced indirect desorption of CH4 provide useful insights for the generalization of this process to other molecules co-existing with CO in ice mantles.
The nature of the bipolar, $\gamma$-ray Fermi bubbles (FB) is still unclear, in part because their faint, high-latitude X-ray counterpart has until now eluded a clear detection. We stack ROSAT data at varying distances from the FB edges, thus boosting the signal and identifying an expanding shell behind the southwest, southeast, and northwest edges, albeit not in the dusty northeast sector near Loop I. A Primakoff-like model for the underlying flow is invoked to show that the signals are consistent with halo gas heated by a strong, forward shock to $\sim$keV temperatures. Assuming ion--electron thermal equilibrium then implies a $\sim10^{56}$ erg event near the Galactic centre $\sim7$ Myr ago. However, the reported high absorption-line velocities suggest a preferential shock-heating of ions, and thus more energetic ($\sim 10^{57}$ erg), younger ($\lesssim 3$ Myr) FBs.
Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, low-frequency radio interferometers. We investigate the feasibility of combining low-frequency observations with the Square Kilometre Array and near infra-red survey data of the Wide-Field Infrared Survey Telescope to detect cosmic reionization by imaging HII bubbles surrounding massive galaxies during the cosmic dawn. While individual bubbles will be too small to be detected, we find that by stacking redshifted 21-cm spectra centred on known galaxies, it will be possible to directly detect the EoR at $z \sim 9-12$, and to place qualitative constraints on the evolution of the spin temperature of the intergalactic medium (IGM) at $z \geq 9$. In particular, given a detection of ionized bubbles using this technique, it is possible to determine if the IGM surrounding them is typically in absorption or emission. Determining the globally-averaged neutral fraction of the IGM using this method will prove more difficult due to degeneracy with the average size of HII regions.
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The assessment of the relationship between radio continuum luminosity and star formation rate (SFR) is of crucial importance to make reliable predictions for the forthcoming ultra-deep radio surveys and to allow a full exploitation of their results to measure the cosmic star formation history. We have addressed this issue by matching recent accurate determinations of the SFR function up to high redshifts with literature estimates of the 1.4 GHz luminosity functions of star forming galaxies (SFGs). This was done considering two options, proposed in the literature, for the relationship between the synchrotron emission ($L_{\rm synch}$), that dominates at 1.4 GHz, and the SFR: a linear relation with a decline of the $L_{\rm synch}$/SFR ratio at low luminosities or a mildly non-linear relation at all luminosities. In both cases we get good agreement with the observed radio luminosity functions but, in the non-linear case, the deviation from linearity must be small. The luminosity function data are consistent with a moderate increase of the $L_{\rm synch}$/SFR ratio with increasing redshift, indicated by other data sets, although a constant ratio cannot be ruled out. A stronger indication of such increase is provided by recent deep 1.4 GHz counts, down to $\mu$Jy levels. This is in contradiction with models predicting a decrease of that ratio due to inverse Compton cooling of relativistic electrons at high redshifts. Synchrotron losses appear to dominate up to $z\simeq 5$. We have also updated the Massardi et al. (2010) evolutionary model for radio loud AGNs.
We propose a new methodology aimed at finding star-forming galaxies in the phase which immediately follows the star-formation (SF) quenching, based on the use of high- to low-ionization emission line ratios. These ratios rapidly disappear after the SF halt, due to the softening of the UV ionizing radiation. We focus on [O III] $\lambda$5007/H$\alpha$ and [Ne III] $\lambda$3869/[O II] $\lambda$3727, studying them with simulations obtained with the CLOUDY photoionization code. If a sharp quenching is assumed, we find that the two ratios are very sensitive tracers as they drop by a factor $\sim$ 10 within $\sim$ 10 Myr from the interruption of the SF; instead, if a smoother and slower SF decline is assumed (i.e. an exponentially declining star-formation history with $e$-folding time $\tau=$ 200 Myr), they decrease by a factor $\sim$ 2 within $\sim$ 80 Myr. We mitigate the ionization -- metallicity degeneracy affecting our methodology using pairs of emission line ratios separately related to metallicity and ionization, adopting the [N II] $\lambda$6584/[O II] $\lambda$3727 ratio as metallicity diagnostic. Using a Sloan Digital Sky Survey galaxy sample, we identify 10 examples among the most extreme quenching candidates within the [O III] $\lambda$5007/H$\alpha$ vs. [N II] $\lambda$6584/[O II] $\lambda$3727 plane, characterized by low [O III] $\lambda$5007/H$\alpha$, faint [Ne III] $\lambda$3869, and by blue dust-corrected spectra and $(u-r)$ colours, as expected if the SF quenching has occurred in the very recent past. Our results also suggest that the observed fractions of quenching candidates can be used to constrain the quenching mechanism at work and its time-scales.
We use the first Gaia data release, combined with RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within <~3 kpc from the Sun. We identify halo stars kinematically, as moving with a relative speed of at least 220 km/s with respect to the local standard of rest. These stars are in general more metal-poor than the disk, but surprisingly, half of our halo sample is comprised of stars with [Fe/H]>-1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the isotropic orbital distribution of the more metal-poor halo stars. We find similar properties in the Latte cosmological zoom-in simulation of a Milky Way-like galaxy from the FIRE project. In Latte, metal-rich halo stars formed primarily inside of the solar circle, while lower-metallicity halo stars preferentially formed at larger distances (extending beyond the virial radius). This suggests that metal-rich halo stars in the Solar neighborhood in fact formed in-situ within the Galactic disk rather than having been accreted from satellite systems. These stars, currently on halo-like orbits, therefore have likely undergone substantial radial migration/heating.
We study the effect of a fluctuating active galactic nucleus (AGN) on the abundance of circumgalactic OVI in galaxies selected from the EAGLE simulations. We follow the time-variable OVI abundance in post-processing around four galaxies - two at $z=0.1$ with stellar masses of $M_{\ast} \sim 10^{10}$ M$_{\odot}$ and $M_{\ast} \sim 10^{11}$ M$_{\odot}$, and two at $z=3$ with similar stellar masses - out to impact parameters of twice their virial radii, implementing a fluctuating source of ionizing radiation in their centres. Due to delayed recombination, the AGN leave significant `AGN proximity zone fossils' around all four galaxies, where OVI and other metal ions are out of ionization equilibrium for several megayears after the AGN fade. The column density of OVI is typically enhanced by $\approx 0.3-1.0$ dex at impact parameters within $0.3R_{\rm vir}$, and by $\approx 0.06-0.2$ dex at $2R_{\rm vir}$, thereby also enhancing the covering fraction of OVI above a given column density threshold. The strength of the AGN fossil effect depends on the flux of ionizing photons, the abundance of low-state oxygen ions (OI - OV) and the gas density. The fossil effect tends to increase with increasing AGN luminosity, and towards shorter AGN lifetimes and larger AGN duty cycle fractions, as the time in between subsequent AGN-on phases decreases. In the limit of short AGN lifetimes, the effect converges to that of a continuous AGN with a luminosity of $(f_{\rm duty}/100\%)$ times the AGN luminosity. We also find significant fossil effects for other metal ions, where low-ionization state ions are decreased (SiIV, CIV at $z=3$) and high-ionization state ions are increased (CIV at $z=0.1$, NeVIII, MgX). Using observationally motivated AGN parameters, we predict AGN proximity zone fossils to be ubiquitous around $M_{\ast} \sim 10^{10-11}$ M$_{\odot}$ galaxies, and to affect the observations of metals [...]
We present clustering analyses of identically-selected star-forming galaxies in 3 narrow redshift slices (at z=0.8, z=1.47 and z=2.23), from HiZELS, a deep, near-infrared narrow-band survey. The HiZELS samples span the peak in the cosmic star-formation rate density, identifying typical star-forming galaxies at each epoch. Narrow-band samples have well-defined redshift distributions and are therefore ideal for clustering analyses. We quantify the clustering of the three samples, and of H-alpha luminosity-selected subsamples, initially using simple power law fits to the two-point correlation function. We extend this work to link the evolution of star-forming galaxies and their host dark matter halos over cosmic time using sophisticated dark matter halo models. We find that the clustering strength, r0, and the bias of galaxy populations relative to the clustering of dark matter increase linearly with H-alpha luminosity (and, by implication, star-formation rate) at all three redshifts, as do the host dark matter halo masses of the HiZELS galaxies. The typical galaxies in our samples are star-forming centrals, residing in halos of mass M_halo ~ a few times 10^12M_solar. We find a remarkably tight redshift-independent relation between the H-alpha luminosity scaled by the characteristic luminosity, L(H-alpha)/L(H-alpha)*(z), and the minimum host dark matter halo mass of central galaxies. This reveals that the dark matter halo environment is a strong driver of galaxy star-formation rate and therefore of the evolution of the star-formation rate density in the Universe.
The peculiar nature of the host galaxy of the low-luminosity GRB 100316D has baffled the astronomers since its first detection. The low distance, $z=0.0591$, of GRB 100316D and its association with SN 2010bh represent two important motivations for studying this host galaxy and the GRB's immediate environment with the high spatial resolution provided by the VLT/MUSE. Its large field-of-view allows us to create 2D maps of gas metallicity, ionization level and the star-formation rate distribution maps. Based on these, we derive that the GRB exploded in the most active star-forming region of the galaxy, characterized by a low metallicity and a young stellar population. We conclude that the host is a late-type dwarf galaxy characterized by the presence of multiple star-forming regions and an extended central region with on-going shock interactions. The galaxy likely experienced a relatively recent gravitational encounter, that also triggered an intense burst of star-formation 5-15 Myr ago, generating a massive stellar population (including stars with masses up to 20 -- 40 $M_{\odot}$) at the GRB site.
We have carried out a systematic search for recoiling supermassive black holes (rSMBH) using the Chandra Source and SDSS Cross Matched Catalog. From the survey, we have detected a potential rSMBH, 'CXO J101527.2+625911' at z=0.3504. The CXO J101527.2+625911 has a spatially offset (1.26$\pm$0.05 kpc) active SMBH and kinematically offset broad emission lines (175$\pm$25 km s$^{\rm -1}$ relative to systemic velocity). The observed spatial and velocity offsets suggest this galaxy could be a rSMBH, but we also have considered a possibility of dual SMBH scenario. The column density towards the galaxy center was found to be Compton thin, but no X-ray source was detected. The non-detection of the X-ray source in the nucleus suggests either there is no obscured actively accreting SMBH, or there exists an SMBH but has a low accretion rate (i.e. low-luminosity AGN (LLAGN)). The possibility of the LLAGN was investigated and found to be unlikely based on the H$\alpha$ luminosity, radio power, and kinematic arguments. This, along with the null detection of X-ray source in the nucleus supports our hypothesis that the CXO J101527.2+625911 is a rSMBH. Our GALFIT analysis shows the host galaxy to be a bulge-dominated elliptical. The weak morphological disturbance and small spatial and velocity offsets suggest that CXO J101527.2+625911 could be in the final stage of merging process and about to turn into a normal elliptical galaxy.
Evidence for dust around supermassive black holes (SMBHs) in the early Universe is strongly suggested by recent observations. However, the accretion mechanism of SMBHs in dusty gas is not well understood yet. We investigate the growth of intermediate-mass black-holes (IMBHs) of $\sim 10^{5}~M_{\odot}$ in dusty clouds by using one-dimensional radiative-hydrodynamics simulations. We find that the accretion of dusty gas onto IMBHs proceeds gently with small fluctuations of the accretion rate, whereas that of pristine gas causes more violent periodic bursts. At dust-to-gas mass ratios similar to the solar neighborhood, the time averaged luminosity becomes smaller than that for primordial gas by one order of magnitude and the time-averaged Eddington ratio ranges from $\sim 10^{-4}$ to $\sim 10^{-2}$ in clouds with initial gas densities of $n_{\rm H} = 10 - 1000~\rm cm^{-3}$. Our calculations show that the effect of dust opacity alone is secondary compared to the radiation pressure on dust in regulating the BH growth. We also derive spectral energy distributions at IR bands by calculating dust thermal emission and show that the flux ratio between $\lambda \lesssim 20~\rm \mu m$ and $\gtrsim 100~\rm \mu m$ is closely related to the Eddington ratio. Thermal emission from hot dust near the BH dominates only during the high accretion phase, producing higher flux density at $\lesssim 20~\rm \mu m$. Therefore, we suggest that the combinations of MIR observations by JWST and FIR observation by ALMA or Spitzer can be used to estimate the Eddington ratio of massive BHs.
Many nearby AGNs display a significant short-term variability. In this work we re-analyze photometric data of four active galactic nuclei observed by Kepler in order to study the flickering activity, having as main goal that of searching for multiple components in the power density spectra. We find that all four objects have similar characteristics, with two break frequencies at approximately log(f/Hz)=-5.2 and -4.7. We consider some physical phenomena whose characteristic time-scales are consistent with those observed, in particular mass accretion fluctuations in the inner geometrically thick disc (hot X-ray corona) and unstable relativistic Rayleigh-Taylor modes. The former is supported by detection of the same break frequencies in the Swift X-ray data of ZW229-15. We also discuss rms-flux relations, and we detect a possible typical linear trend at lower flux levels. Our findings support the hypothesis of a multiplicative character of variability, in agreement with the propagating accretion fluctuation model.
Rate-equation models are a widely-used and inexpensive tool for the simulation of interstellar chemistry under a range of physical conditions. However, their application to grain-surface chemical systems necessitates a number of simplifying assumptions, due to the requirement to treat only the total population of each species, using averaged rates, rather than treating each surface particle as an independent entity. While the outputs from rate-equation models are strictly limited to such population information, the inputs -- in the form of the averaged rates that control the time-evolution of chemical populations -- can be guided by the results from more exact simulation methods. Here, we examine the effects of back-diffusion, wherein particles diffusing on a surface revisit binding sites on the lattice, slowing the total reaction rate. While this effect has been studied for two-particle systems, its influence at greater surface coverage of reactants has not been explored. Results from two Monte Carlo kinetics models (one a 2-D periodic lattice, the other the surface of a three dimensionally-realized grain) were used to develop a means to incorporate the grain-surface back-diffusion effect into rate-equation methods. The effects of grain size, grain morphology, and surface coverage on the magnitude of the back-diffusion effect were studied for the simple H+H reaction system. The results were fit with expressions that can be easily incorporated into astrochemical rate-equation models to reproduce accurately the effects of back-diffusion on grain-surface reaction rates. Back-diffusion reduces reaction rates by a maximum factor of around 5 for the canonical grain of $\sim$10$^6$ surface sites, but this falls to unity at close to full surface coverage.
The CIBER collaboration released their first observational data of the Cosmic IR background (CIB) radiation, which has significant excesses at around the wavelength $\sim$ 1 $\mu$m compared to theoretically-inferred values. The amount of the CIB radiation has a significant influence on the opaqueness of the Universe for TeV gamma-rays emitted from distant sources such as AGNs. With the value of CIB radiation reported by the CIBER experiment, through the reaction of such TeV gamma-rays with the CIB photons, the TeV gamma-rays should be significantly attenuated during propagation, which would lead to energy spectra in disagreement with current observations of TeV gamma ray sources. In this article, we discuss a possible resolution of this tension between the TeV gamma-ray observations and the CIB data in terms of axion [or Axion-Like Particles (ALPs)] that may increase the transparency of the Universe by the anomaly-induced photon-axion mixing. We find a region in the parameter space of the axion mass, $m_a \sim 5 \times 10^{-10} - 3 \times 10^{-7}$eV, and the axion-photon coupling constant, $1.2 \times 10^{-11} {\rm GeV}^{-1} \lesssim g_{a\gamma} \lesssim 8.8 \times 10^{-10} {\rm GeV}^{-1}$ that solves this problem.
Current constraints on models of galaxy evolution rely on morphometric catalogs extracted from multi-band photometric surveys. However, these catalogs are altered by selection effects that are diffcult to model, correlate in non trivial ways and can lead to contradictory predictions if not taken into account carefully. To address this issue, we have developed a new approach combining Approximate Bayesian Computation techniques and empirical modeling with realistic image simulations that reproduce a large fraction of these selection effects. This allows us to perform a direct comparison between observed and simulated images and to infer robust constraints on model parameters. We use a semi-empirical forward model to generate a distribution of mock galaxies from a set of physical parameters. These galaxies are passed through an image simulator reproducing the instrumental characteristics of any survey, and are then extracted in the same way as the observed data. The discrepancy between the simulated and observed data is quantified with a distance metric, and minimized with a custom sampling process based on adaptive Monte Carlo Markov Chain methods. Using synthetic data matching most of the properties of a CFHTLS Deep field, we demonstrate the robustness and internal consistency of our approach by inferring the parameters governing the size and luminosity functions and their evolutions for different realistic populations of galaxies. We also compare the results of our approach with those obtained from the classical SED fitting and photometric redshift approach. Our pipeline infers effciently the luminosity and size distribution and evolution parameters with a very limited number of observables (3 photometric bands). When compared to SED fitting based on the same set of observables, our method yields results that are more accurate and free from systematics biases.
We have compiled a new multiwavelength spectral energy distribution (SED) for the closest obscured low-ionization emission-line region active galactic nucleus (AGN), NGC 4736, also known as M94. The SED comprises mainly high-resolution (mostly sub-arcsecond, or, at the distance to M94, <23 pc from the nucleus) observations from the literature, archival data, as well as previously unpublished sub-millimetre data from the Plateau de Bure Interferometer (PdBI) and the Combined Array for Research in Millimeter-wave Astronomy, in conjunction with new electronic MultiElement Radio Interferometric Network (e-MERLIN) L-band (1.5 GHz) observations. Thanks to the e-MERLIN resolution and sensitivity, we resolve for the first time a double structure composed of two radio sources separated by ~1 arcsec, previously observed only at higher frequency. We explore this data set, which further includes non-simultaneous data from the Very Large Array, the Gemini telescope, the Hubble Space Telescope and the Chandra X-ray observatory, in terms of an outflow-dominated model. We compare our results with previous trends found for other AGN using the same model (NGC 4051, M81*, M87 and Sgr A*), as well as hard- and quiescent-state X-ray binaries. We find that the nuclear broad-band spectrum of M94 is consistent with a relativistic outflow of low inclination. The findings in this work add to the growing body of evidence that the physics of weakly accreting black holes scales with mass in a rather straightforward fashion.
We present a novel analysis of the metal-poor star sample in the complete Radial Velocity Experiment (RAVE) Data Release 5 catalog with the goal of identifying and characterizing all very metal-poor stars observed by the survey. Using a three-stage method, we first identified the candidate stars using only their spectra as input information. We employed an algorithm called t-SNE to construct a low-dimensional projection of the spectrum space and isolate the region containing metal-poor stars. Following this step, we measured the equivalent widths of the near-infrared CaII triplet lines with a method based on flexible Gaussian processes to model the correlated noise present in the spectra. In the last step, we constructed a calibration relation that converts the measured equivalent widths and the color information coming from the 2MASS and WISE surveys into metallicity and temperature estimates. We identified 877 stars with at least a 50% probability of being very metal-poor $(\rm [Fe/H] < -2\,\rm dex)$, out of which 43 are likely extremely metal-poor $(\rm [Fe/H] < -3\,\rm dex )$. The comparison of the derived values to a small subsample of stars with literature metallicity values shows that our method works reliably and correctly estimates the uncertainties, which typically have values $\sigma_{\rm [Fe/H]} \approx 0.2\,\mathrm{dex}$. In addition, when compared to the metallicity results derived using the RAVE DR5 pipeline, it is evident that we achieve better accuracy than the pipeline and therefore more reliably evaluate the very metal-poor subsample. Based on the repeated observations of the same stars, our method gives very consistent results. The method used in this work can also easily be extended to other large-scale data sets, including to the data from the Gaia mission and the upcoming 4MOST survey.
Silicon carbide (SiC) grains are a major dust component in carbon-rich AGB
stars. The formation pathways of these grains are, however, not fully
understood.\ We calculate ground states and energetically low-lying structures
of (SiC)$_n$, $n=1,16$ clusters by means of simulated annealing (SA) and Monte
Carlo simulations of seed structures and subsequent quantum-mechanical
calculations on the density functional level of theory. We derive the infrared
(IR) spectra of these clusters and compare the IR signatures to observational
and laboratory data.\ According to energetic considerations, we evaluate the
viability of SiC cluster growth at several densities and temperatures,
characterising various locations and evolutionary states in circumstellar
envelopes.\ We discover new, energetically low-lying structures for
Si$_{4}$C$_{4}$, Si$_{5}$C$_{5}$, Si$_{15}$C$_{15}$ and Si$_{16}$C$_{16}$, and
new ground states for Si$_{10}$C$_{10}$ and Si$_{15}$C$_{15}$. The clusters
with carbon-segregated substructures tend to be more stable by 4-9 eV than
their bulk-like isomers with alternating Si-C bonds. However, we find ground
states with cage ("bucky"-like) geometries for Si$_{12}$C$_{12}$ and
Si$_{16}$C$_{16}$ and low-lying, stable cage structures for n $\ge$ 12. The
latter findings indicate thus a regime of clusters sizes that differs from
small clusters as well as from large-scale crystals. Thus, and owing to their
stability and geometry, the latter clusters may mark a transition from a
quantum-confined cluster regime to crystalline, solid bulk-material.
The calculated vibrational IR spectra of the ground-state SiC clusters shows
significant emission. They include the 10-13 $\mu$m wavelength range and the
11.3 $\mu$m feature inferred from laboratory measurements and observations,
respectively, though the overall intensities are rather low.
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Magnetic fields in galaxies are believed to be the result of dynamo
amplification of initially weak seed fields, reaching equipartition strength
inside the interstellar medium. The small-scale dynamo appears to be a viable
mechanism to explain observations of strong magnetic fields in present-day and
high-redshift galaxies, considering the extreme weakness of seed fields
predicted by battery mechanisms or primordial fields. Performing
high-resolution adaptive mesh magneto-hydrodynamic simulations of a small mass,
isolated cooling halo with an initial magnetic seed field strength well below
equipartition, we follow the small-scale dynamo amplification from
supernova-induced turbulence up to saturation of the field. We find that
saturation occurs when the average magnetic pressure reaches only 3 % to 5 % of
the turbulent pressure. The magnetic energy growth transitions from exponential
to linear, and finally comes to halt. The saturation level increases slightly
with grid resolution. These results are in good agreement with theoretical
predictions for magnetic Prandtl numbers of order $\mathrm{Pr_M} \sim 1$ and
turbulent Mach numbers of order $\mathrm{M} \sim 10$. When we suppress
supernova feedback after our simulation has reached saturation, we find that
turbulence decays and that the gas falls back onto a thin disk with the
magnetic field in local equipartition.
We propose a scenario in which galactic magnetic fields are amplified from
weak seed fields in the early stages of the Universe to sub-equipartition
fields, owing to the turbulent environment of feedback-dominated galaxies at
high redshift, and are evolved further in a later stage up to equipartition, as
galaxies transformed into more quiescent, large spiral disks.
The Galactic Centre (GC) is a unique place to study the extreme dynamical processes occurring near a super-massive black hole (SMBH). Here we investigate the role of supernova (SN) explosions occurring in massive binary systems lying in a disc-like structure within the innermost parsec. We use a regularized algorithm to simulate 30,000 isolated three-body systems composed of a stellar binary orbiting the SMBH. We start the integration when the primary member undergoes a SN explosion, and we analyze the impact of SN kicks on the orbits of stars and compact remnants. We find that SN explosions scatter the lighter stars in the pair on completely different orbits, with higher eccentricity and inclination. In contrast, stellar-mass black holes (BHs) and massive stars retain memory of the orbit of their progenitor star. Our results suggest that SN kicks are not sufficient to eject BHs from the GC. We thus predict that all BHs that form in situ in the central parsec of our Galaxy remain in the GC, building up a cluster of dark remnants. In addition, the change of NS orbits induced by SNe may partially account for the observed dearth of NSs in the GC. About 40 per cent of remnants stay bound to the stellar companion after the kick; we expect up to 70 per cent of them might become X-ray binaries through Roche-lobe filling. Finally, the eccentricity of some light stars becomes > 0.7 as an effect of the SN kick, producing orbits similar to those of the G1 and G2 dusty objects.
We present an analysis of high-resolution ALMA interferometry of CO(4-3) line emission and dust continuum in the "Ruby" (PLCK_G244.8+54.9), a bright, gravitationally lensed galaxy at z = 3.0 discovered with the Planck all-sky survey. The Ruby is the brightest of Planck's Dusty GEMS, a sample of 11 of the brightest gravitationally lensed high-redshift galaxies on the extragalactic sub-mm sky. We resolve the high-surface-brightness continuum and CO line emission of the Ruby in several extended clumps along a partial, nearly circular Einstein ring with 1.4" diameter around a massive galaxy at z = 1.5. Local star-formation intensities are up to 4000 M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$, amongst the highest observed at high redshift, and clearly in the range of maximal starbursts. Gas-mass surface densities are a few $\times$ 10$^4$ M$_{\odot}$ pc$^{-2}$. The Ruby lies at, and in part even above, the starburst sequence in the Schmidt-Kennicutt diagram, and at the limit expected for star formation that is self-regulated through the kinetic energy injection from radiation pressure, stellar winds, and supernovae. We show that these processes can also inject sufficient kinetic energy and momentum into the gas to explain the turbulent line widths, which are consistent with marginally gravitationally bound molecular clouds embedded in a critically Toomre-stable disk. The star-formation efficiency is in the range 1-10% per free-fall time, consistent with the notion that the pressure balance that sets the local star-formation law in the Milky Way may well be universal out to the highest star-formation intensities. AGN feedback is not necessary to regulate the star formation in the Ruby, in agreement with the absence of a bright AGN component in the infrared and radio regimes.
We present spectroscopic identification of 32 new quasars and luminous galaxies discovered at 5.7 < z < 6.8. This is the second in a series of papers presenting the results of the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multi-band imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The photometric candidates were selected by a Bayesian probabilistic algorithm, and then observed with spectrographs on the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous paper, we have now identified 64 HSC sources over about 430 deg2, which include 33 high-z quasars, 14 high-z luminous galaxies, 2 [O III] emitters at z ~ 0.8, and 15 Galactic brown dwarfs. The new quasars have considerably lower luminosity (M1450 ~ -25 to -22 mag) than most of the previously known high-z quasars. Several of these quasars have luminous (> 10^(43) erg/s) and narrow (< 500 km/s) Ly alpha lines, and also a possible mini broad absorption line system of N V 1240 in the composite spectrum, which clearly separate them from typical quasars. On the other hand, the high-z galaxies have extremely high luminosity (M1450 ~ -24 to -22 mag) compared to other galaxies found at similar redshift. With the discovery of these new classes of objects, we are opening up new parameter spaces in the high-z Universe. Further survey observations and follow-up studies of the identified objects, including the construction of the quasar luminosity function at z ~ 6, are ongoing.
The Galaxy Evolution Explorer (GALEX) imaged the sky in two Ultraviolet (UV)
bands, far-UV (FUV) and near-UV (NUV), delivering the first comprehensive sky
surveys at these wavelengths. The GALEX database contains FUV and NUV images,
500~million source measurements and over 100,000 low-resolution UV spectra.
[...] We present science-enhanced, clean catalogs of GALEX UV sources, with
useful tags to facilitate scientific investigations. The catalogs are an
improved and expanded version of our previous catalogs of UV sources (Bianchi
et al. 2011, 2014: BCScat). With respect to BCScat, we have patched 640 fields
for which the pipeline had improperly coadded non-overlapping observations, we
provide a version with a larger sky coverage (about 10percent) [...]. We added
new tags to facilitate selection and cleaning of statistical samples...: we
flag sources within the footprint of extended objects (nearby galaxies, stellar
clusters) so that these regions can be excluded for estimating source density.
As in our previous catalogs, in GUVcat duplicate measurements of the same
source are removed.[...] Such unique-source catalog is needed to study density
and distributions of sources, and to match UV sources with catalogs at other
wavelengths. The catalog includes all observations from the All-Sky Imaging
Survey (AIS), the survey with the largest area coverage, with both FUV and NUV
detectors exposed: over 28,700 fields, made up of a total of 57,000
observations ("visits"). The total area covered, when overlaps are removed and
gaps accounted for, is 24,790 (GUVcat_AIS_fov055) and 22,125
(GUVcat_AIS_fov050) square degrees. The total number of unique AIS sources
(eliminating duplicate measurements) is 82,992,086 (GUVcat_AIS_fov055) and
69,772,677 (GUVcat_AIS_fov050).
The typical depth of the GUVcat_AIS catalog is FUV=19.9, NUV=20.8ABmag.
We present the results of a set of N-body simulations following the long-term
evolution of the rotational properties of star cluster models evolving in the
external tidal field of their host galaxy, after an initial phase of violent
relaxation. The effects of two-body relaxation and escape of stars lead to a
redistribution of the ordered kinetic energy from the inner to the outer
regions, ultimately determining a progressive general loss of angular momentum;
these effects are reflected in the overall decline the rotation curve as the
cluster evolves and loses stars.
We show that all of our models share the same dependence of the remaining
fraction of the initial rotation on the fraction of the initial mass lost. As
the cluster evolves and loses part of its initial angular momentum, it becomes
increasingly dominated by random motions, but even after several tens of
relaxation times, and losing a significant fraction of its initial mass, a
cluster can still be characterized by a non-negligible ratio of the rotational
velocity to the velocity dispersion. This result is in qualitative agreement
with the recently observed kinematical complexity which characterizes several
Galactic globular clusters.
ABRIGED: Quantifying the number, type and distribution of W-R stars is a key component in the context of galaxy evolution, since they put constraints on the age of the star formation bursts. Nearby galaxies (d<5 Mpc) are particularly relevant in this context since they fill the gap between studies in the Local Group, where individual stars can be resolved, and galaxies in the Local Volume and beyond. We intend to characterize the W-R star population in NGC625, a low-metallicity dwarf galaxy suffering a currently declining burst of star formation. Optical IFS data have been obtained with the VIMOS-IFU covering the starburst region. We estimate the number of W-R stars using a linear combination of 3 W-R templates: 1 early-type nitrogen (WN) star, 1 late-type WN star and 1 carbon-type (WC) star (or oxygen-type (WO) star). Fits using several ensembles of templates were tested. Results were confronted with: i) high spatial resolution HST photometry; ii) numbers of W-R stars in nearby galaxies; iii) model predictions. The W-R star population is spread over the main body of the galaxy, not necessarily coincident with the overall stellar distribution. Our best estimation for the number of W-R stars yields a total of 28 W-R stars in the galaxy, out of which 17 are early- type WN, 6 are late-type WN and 5 are WC stars. The width of the stellar features nicely correlates with the dominant W-R type found in each aperture. The distribution of the different types of WR in the galaxy is roughly compatible with the way star formation has propagated in the galaxy, according to previous findings using HST images. Fits using templates at the metallicity of the LMC yield more reasonable number of W-R than those using templates at the metallicity of the SMC. Given the metallicity of NGC 625, this suggests a non-linear relation between the metallicity and the luminosity of the W-R spectral features.
Low- and intermediate mass galaxies are widely discussed as cause of reionization at redshift $z\sim10-6$. However, observational proof of galaxies that are leaking ionizing radiation (Lyman continuum; LyC) is a currently ongoing challenge and the list of LyC emitting candidates is still short. Tololo 1247-232 is among those very few galaxies with recently reported leakage. We performed intermediate resolution ultraviolet (UV) spectroscopy with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope and confirm ionizing radiation emerging from Tololo 1247-232. Adopting an improved data reduction procedure, we find that LyC escapes from the central stellar clusters, with an escape fraction of 1.5$\pm$0.5% only, i.e. the lowest value reported for the galaxy so far. We further make use of FUV absorption lines of Si II and Si IV as a probe of the neutral and ionized interstellar medium. We find that most of the ISM gas is ionized, likely facilitating LyC escape from density bounded regions. Neutral gas covering as a function of line-of-sight velocity is derived using the apparent optical depth method. The ISM is found to be sufficiently clumpy, supporting the direct escape of LyC photons. We further report on broadband UV and optical continuum imaging as well as narrowband imaging of Ly$\alpha$, H$\alpha$ and H$\beta$. Using stellar population synthesis, a Ly$\alpha$ escape fraction of 8% was derived. We also performed VLA 21cm imaging. The hydrogen hyperfine transition was not detected, but a deep upper limit atomic gas mass of $\lesssim10^9 M_{\odot}$ could be derived. The upper limit gas fraction defined as $\frac{M_{H I}}{M_*}$ is only 20%. Evidence is found that the H I gas halo is relatively small compared to other Lyman Alpha emitters.
We present the near-infrared high resolution imaging of an extremely dense group of galaxies at the core of the protocluster at $z=3.09$ in the SSA22 field by using the adaptive optics AO188 and the Infrared Camera and Spectrograph (IRCS) on Subaru Telescope. Wide morphological variety of them suggests their on-going dramatic evolutions. One of the two quiescent galaxies (QGs), the most massive one in the group, is a compact elliptical with an effective radius $r_{e} = 1.37\pm0.75$ kpc. It supports the two-phase formation scenario of giant ellipticals today that a massive compact elliptical is formed at once and evolves in the size and stellar mass by series of mergers. Since this object is a plausible progenitor of a brightest cluster galaxy (BCG) of one of the most massive clusters today, it requires strong size ($\ga10$) and stellar mass ($\sim$ four times by $z=0$) growths. Another QG hosts an AGN(s) and is fitted with a model composed from an nuclear component and S\'ersic model. It shows spatially extended [O{\footnotesize III}]$\lambda$5007 emission line compared to the continuum emission, a plausible evidence of outflows. Massive star forming galaxies (SFGs) in the group are two to three times larger than the field SFGs at similar redshift. Although we obtained the $K$-band image deeper than the previous one, we found no candidate new members. This implies a physical deficiency of low mass galaxies with stellar mass $M_{\star}\la4\times10^{10}~M_{\odot}$ and/or poor detection completeness of them owing to their diffuse morphologies.
An interesting transient has been detected in one of our three Dark Energy Camera deep fields. Observations of these deep fields take advantage of the high red sensitivity of DECam on the Cerro Tololo Interamerican Observatory Blanco telescope. The survey includes the Y band with rest wavelength 1430{\AA} at z = 6. Survey fields (the Prime field 0555-6130, the 16hr field 1600-75 and the SUDSS New Southern Field) are deeper in Y than other infrared surveys. They are circumpolar, allowing all night to be used efficiently, exploiting the moon tolerance of 1 micron observations to minimize conflict with the Dark Energy Survey. As an i-band dropout (meaning that the flux decrement shortward of Lyman alpha is in the i bandpass), the transient we report here is a supernova candidate with z ~ 6, with a luminosity comparable to the brightest known current epoch superluminous supernova (i.e., ~ 2 x 10^11 solar luminosities).
We have measured the clustering of galaxies around active galactic nuclei (AGN) for which single-epoch virial masses of the super-massive black hole (SMBH) are available to investigate the relation between the large scale environment of AGNs and the evolution of SMBHs. The AGN samples used in this work were derived from the Sloan Digital Sky Survey (SDSS) observations and the galaxy samples were from 250deg$^{2}$ S15b data of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). The investigated redshift range is 0.6--3.0, and the masses of the SMBHs lie in the range $10^{7.5}$--$10^{10}$$M_{\rm sun}$. The absolute magnitude of the galaxy samples reaches to $M_{\rm 320}$ $\sim$ $-$18 at rest frame wavelength 320nm for the low-redshift end of the samples. More than 70\% of the galaxies in the analysis are blue. We found a significant dependence of the cross-correlation length on redshift, which primarily reflects the brightness dependence of the galaxy clustering. At the lowest redshifts the cross-correlation length increases from 7$h^{-1}$Mpc around $M_{\rm 320} = $ $-19$mag to $>$10$h^{-1}$Mpc beyond $M_{\rm 320} = $ $-20$mag. No significant dependence of the cross-correlation length on BH mass was found for whole galaxy samples dominated by blue galaxies, while there was an indication of BH mass dependence in the cross-correlation with red galaxies. These results provides us a picture that the environment of AGNs studied in this paper is enriched with blue starforming galaxies, and a fraction of the galaxies are being evolved to red galaxies along with the evolution of SMBHs in that system.
We present the results from a search for new Milky Way (MW) satellites from the first two years of data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) $\sim 300$~deg$^2$ and report the discovery of an ultra-faint dwarf galaxy in Cetus. This is the second ultra-faint dwarf we have discovered after Virgo~I reported in our previous paper. This new satellite, Cetus~III, has been identified as a statistically significant (10.7$\sigma$) spatial overdensity of star-like objects, which are selected from a relevant isochrone filter designed for a metal-poor and old stellar population. This stellar system is located at a heliocentric distance of 251$^{+24}_{-11}$~kpc with a most likely absolute magnitude of $M_V = -2.4 \pm 0.6$~mag estimated from a Monte Carlo analysis. Cetus~III is extended with a half-light radius of $r_h = 90^{+42}_{-17}$~pc, suggesting that this is a faint dwarf satellite in the MW located beyond the detection limit of the Sloan Digital Sky Survey. We also revisit and update the parameters for Virgo~I finding $M_V = -0.33^{+0.75}_{-0.87}$~mag and $r_h = 47^{+19}_{-13}$~pc. Using simulations of $\Lambda$-dominated cold dark matter models, we predict that we should find one or two new MW satellites from $\sim 300$~deg$^2$ HSC-SSP data, in rough agreement with the discovery rate so far. The further survey and completion of HSC-SSP over $\sim 1,400$~deg$^2$ will provide robust insights into the missing satellites problem.
We present initial results from the Subaru Strategic Program (SSP) with Hyper Suprime-Cam (HSC) on a comprehensive survey of emission line galaxies at $z<1.5$. In the first data release of the HSC-SSP, two narrowband data (NB816 and NB921) down to 25.6--25.9 mag at $5 \sigma$ are available over 17 deg$^2$, which allow us to construct unprecedentedly large samples of 18,792 H$\alpha$ emitters at $z \approx$ 0.25 and 0.40, 16,051 [OIII] emitters at $z \approx$ 0.63 and 0.84, and 28,157 [OII] emitters at $z \approx$ 1.19 and 1.47. We reveal the cosmic web on a scale of more than 50 comoving Mpc where some galaxy clusters identified by red sequence galaxies are located on the intersection of filamentary structures of star-forming galaxies. The luminosity functions for the emission line galaxies are consistent with the previous studies, except for the bright end of the luminosity functions for the H$\alpha$ emitters at $z \approx$ 0.25--0.40. This is likely due to small survey volumes probed by previous studies which is sensitive to the cosmic variance. The wide field coverage of the data allows us to overcome the cosmic variance and derive the bright end of the luminosity functions more precisely than the previous studies. We also investigate the stellar mass functions for the H$\alpha$ emitters at $z \approx$ 0.25--0.40 and find that they are consistent with those from the stellar mass limited samples. Thus, our samples of the emission line galaxies are the representative ones of star-forming galaxies at the redshifts probed.
We present the environmental dependence of colour, stellar mass, and star formation (SF) activity in H-alpha-selected galaxies along the huge cosmic web at z=0.4 hosting twin clusters in DEEP2-3 field, discovered by Subaru Strategic Programme of Hyper Suprime-Cam (HSC SSP). By combining photo-z selected galaxies and H-alpha emitters selected with broad-band and narrow-band data of the recent internal data release of HSC SSP (DR1), we confirm that galaxies in higher-density environments or galaxies in the cluster central regions show redder colours. We find that there still remains a colour-density and colour-radius correlation even if we restrict the sample to H-alpha-selected galaxies. We also find an increase of star formation rates (SFR), and possible decline in specific SFRs, amongst H-alpha emitters towards the highest-density environment, primarily driven by the excess of red/massive H-alpha emitters in high-density environment. Finally, we find a hint that pairs of H-alpha emitters located in higher-density environment show redder colours than those in underdense regions, implying that galaxy-galaxy interaction in different environments have different impacts on the properties of SF galaxies.
Photometric redshifts are a key component of many science objectives in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). In this paper, we describe and compare the codes used to compute photometric redshifts for HSC-SSP, how we calibrate them, and the typical accuracy we achieve with HSC five-band photometry (grizy). We introduce a new point estimator based on an improved loss function and demonstrate that it works better than other commonly used estimators. We find that our photo-z's are most accurate at 0.3<z<1.5, where we can straddle the 4000A break. We achieve sigma(dz/(1+z))~0.04 and an outlier rate of about 10% for galaxies down to i=25 within this redshift range, which should enable many science cases for HSC-SSP. We also characterize the accuracy of our redshift probability distribution function (PDF) and discover that some codes over/under-estimate the redshift uncertainties, which have implications for N(z) reconstruction. Our photo-z's for the Deep and UltraDeep layers are available in the public data release, while those for the Wide layer will soon be made available. Both our catalog products (such as point estimates) and full PDFs are available from the data release site, https://hsc-release.mtk.nao.ac.jp/.
We present the luminosity function of z=4 quasars based on the Hyper Suprime-Cam Subaru Strategic Program Wide layer imaging data in the g, r, i, z, and y bands covering 339.8 deg^2. From stellar objects, 1666 z~4 quasar candidates are selected by the g-dropout selection down to i=24.0 mag. Their photometric redshifts cover the redshift range between 3.6 and 4.3 with an average of 3.9. In combination with the quasar sample from the Sloan Digital Sky Survey in the same redshift range, the quasar luminosity function covering the wide luminosity range of M1450=-22 to -29 mag is constructed. It is well described by a double power-law model with a knee at M1450=-25.36+-0.13 mag and a flat faint-end slope with a power-law index of -1.30+-0.05. The knee and faint-end slope show no clear evidence of redshift evolution from those at z~2. The flat slope implies that the UV luminosity density of the quasar population is dominated by the quasars around the knee, and does not support the steeper faint-end slope at higher redshifts reported at z>5. If we convert the M1450 luminosity function to the hard X-ray 2-10keV luminosity function using the relation between UV and X-ray luminosity of quasars and its scatter, the number density of UV-selected quasars matches well with that of the X-ray-selected AGNs above the knee of the luminosity function. Below the knee, the UV-selected quasars show a deficiency compared to the hard X-ray luminosity function. The deficiency can be explained by the lack of obscured AGNs among the UV-selected quasars.
We study the UV luminosity functions (LFs) at $z\sim 4$, $5$, $6,$ and $7$ based on the deep large-area optical images taken by the Hyper Suprime-Cam (HSC) Subaru strategic program (SSP). On the 100 deg$^2$ sky of the HSC SSP data available to date, we make enormous samples consisting of a total of 579,555 dropout candidates at $z\sim 4-7$ by the standard color selection technique, 348 out of which are spectroscopically confirmed by our follow-up spectroscopy and the other studies. We obtain the UV LFs at $z \sim 4-7$ that span a very wide UV luminosity range of $\sim 0.002 - 100 \, L_{\rm UV}^\ast$ ($-26 < M_{\rm UV} < -14$ mag), combining UV LFs of our program and the ultra-deep Hubble Space Telescope legacy surveys. We derive three parameters of the best-fit Schechter function, $\phi^\ast$, $M_{\rm UV}^\ast$, and $\alpha$, of the UV LFs in the magnitude range where the AGN contribution is negligible, and find that $\alpha$ and $\phi^\ast$ decrease from $z\sim 4$ to $7$ with no significant evolution of $M_{\rm UV}^\ast$. Because our HSC SSP data bridge the LFs of galaxies and AGNs with great statistical accuracies, we carefully investigate the bright ends of the galaxy UV LFs that are estimated by the subtraction of the AGN contribution either with the spectroscopy results or the best-fit AGN UV LFs. We find that the bright ends of the galaxy UV LFs cannot be explained by the Schechter function fits at $> 2 \sigma$ significance, and require either double power-law functions or modified Schechter functions considering the gravitational lensing magnification bias.
Atomic data are an important source of systematic uncertainty in our determinations of nebular chemical abundances. However, we do not have good estimates of these uncertainties since it is very difficult to assess the accuracy of the atomic data involved in the calculations. We explore here the size of these uncertainties by using 52 different sets of transition probabilities and collision strengths, and all their possible combinations, to calculate the physical conditions and the total abundances of O, N, S, Ne, Cl, and Ar for a sample of planetary nebulae and H II regions. We find that atomic data variations introduce differences in the derived abundance ratios as low as 0.1$-$0.2 dex at low density, but that reach or surpass 0.6$-$0.8 dex at densities above 10$^{4}$ cm$^{-3}$ in several abundance ratios, like O/H and N/O. Removing from the 52 datasets the four datasets that introduce the largest differences, the total uncertainties are reduced, but high density objects still reach uncertainty factors of four for their values of O/H and N/O. We identify the atomic data that introduce most of the uncertainty, which involves the ions used to determine density, namely, the transition probabilities of the S$^{+}$, O$^{+}$, Cl$^{++}$, and Ar$^{+3}$ density diagnostic lines, and the collision strengths of Ar$^{+3}$. Improved calculations of these data will be needed in order to derive more reliable values of chemical abundances in high density nebulae. In the meantime, our results can be used to estimate the uncertainties introduced by atomic data in nebular abundance determinations.
We construct a sample of X-ray bright optically faint active galactic nuclei by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source catalogs. 53 X-ray sources satisfying i band magnitude fainter than 23.5 mag and X-ray counts with EPIC-PN detector larger than 70 are selected from 9.1 deg^2, and their spectral energy distributions (SEDs) and X-ray spectra are analyzed. 46 objects with an X-ray to i-band flux ratio F_X/F_i>10 are classified as extreme X-ray-to-optical flux sources. SEDs of 48 among 53 are represented by templates of type 2 AGNs or starforming galaxies and show signature of stellar emission from host galaxies in the optical in the source rest frame. Infrared/optical SEDs indicate significant contribution of emission from dust to infrared fluxes and that the central AGN is dust obscured. Photometric redshifts determined from the SEDs are in the range of 0.6-2.5. X-ray spectra are fitted by an absorbed power law model, and the intrinsic absorption column densities are modest (best-fit log N_H = 20.5-23.5 cm^-2 in most cases). The absorption corrected X-ray luminosities are in the range of 6x10^42 - 2x10^45 erg s^-1. 20 objects are classified as type 2 quasars based on X-ray luminsosity and N_H. The optical faintness is explained by a combination of redshifts (mostly z>1.0), strong dust extinction, and in part a large ratio of dust/gas.
Detection of the copious amount of X-ray emission from the dilute hot plasma in galaxy clusters suggests that a substantial fraction of the central intracluster medium (ICM) is cooling radiatively on a time scale much faster than the Hubble time. Theoretical models predict the cooling rate as high as about few hundred to few thousand solar mass per year, which would be then made available for the formation of new stars in the core of these clusters. However, systematic studies of the cores of such clusters failed to detect the expected reservoirs of cooled gas. Thus, the gas in the cores of galaxy clusters is losing substantial amount of energy in the form of X-rays but is not cooling. This in turn point towards the famous cooling flow paradox and hence demands some intermittent heating to balance the cooling over such a long period. Several sources have been suggested to counteract on the cooling of the ICM, however, the AGN feedback appeared to be the most promising and enough energetic source to resist cooling of the ICM in the cores of such clusters. In this presentation I will provide a brief overview on the feedback processes that are involved in the cores of the galaxy clusters with an emphasis on the AGN feedback and its observable signatures.
We present the cross-correlation between 151 luminous quasars ($M_{ \mathrm{UV}} < -26$) and 179 protocluster candidates at $z \sim 3.8$, extracted from the Wide imaging survey ($ \sim 121~ $deg$^2$) performed with a part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at $ > 4 \sigma $. The distributions of the distance between quasars and the nearest protoclusters and the significance of the overdensity at the position of quasars are statistically identical to those found for $g$-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of $g$-dropout galaxies around quasars is slightly higher than that around $g$-dropout galaxies on $1.0 - 2.5$ pMpc scales, while at $ < 0.5$ pMpc that around quasars tends to be lower. We also find that quasars with higher UV-luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which the luminous quasar at $z \sim4 $ resides in structures that are less massive than those expected for the progenitors of today's rich clusters of galaxies, and possibly that luminous quasars may be suppressing star formation in their close vicinity.
We investigate the galaxy overdensity around <2 pMpc-scale quasar pairs at high (z>3) and low (z~1) redshift based on the unprecedentedly wide and deep optical survey of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using the first-year survey data covering effectively ~121 deg2 in full-color and depth, we find two luminous pairs at z~3.6 and 3.3 which reside in $>5 \sigma$ overdense regions of g-dropout galaxies. The projected separations of the two pairs are $R_\perp=$1.75 and 1.04 pMpc, and their velocity offsets are $\Delta V=692$ and $1448$ km s$^{-1}$, respectively. This is in clear contrast to the average quasar environments in the same redshift range as discussed in Uchiyama et al. (2017), and implies that the quasar activity of the two pairs is triggered via major mergers in proto-clusters, unlike the vast majority of isolated quasars in general fields that may turn on due to non-merger events such as bar and disk instabilities. At z~1, we find 37 pairs in the current HSC-Wide coverage with $R_\perp<2$ pMpc and $\Delta V<2300$ km s$^{-1}$ including four from Hennawi et al. (2006). The distribution of the peak overdensity significance within two arcminutes around the pairs has a long tail toward high density ($>4\sigma$) regions. Thanks to the large sample size, we find a statistical evidence that this excess is unique in the pair environments when compared to single quasar and randomly-selected galaxy environments. Moreover, there are nine small-scale pairs with $R_\perp<1$ pMpc, two of which are found to reside in cluster fields. Our results demonstrate that quasar pairs at z~1-4 tend to occur in massive haloes, although perhaps not the most massive ones, and that they can be used to search for rare density peaks especially at high redshifts.
There is growing observational evidence of dust coagulation in the dense filaments within molecular clouds. Infrared observations show that the dust grains size distribution gets shallower and the relative fraction of small to large dust grains decreases as the local density increases. Ultraviolet (UV) observations show that the strength of the 2175 {\AA} feature, the so-called UV bump, also decreases with cloud density. In this work, we apply the technique developed for the Taurus study to the Orion molecular cloud and confirm that the UV bump decreases over the densest cores of the cloud as well as in the heavily UV irradiated {\lambda} Orionis shell. The study has been extended to the Rosette cloud with uncertain results given the distance (1.3 kpc).
We study the formation of massive black holes in the first star clusters. We first locate star-forming gas clouds in proto-galactic halos of $\gtrsim10^7~M_{\odot}$ in cosmological hydrodynamics simulations and use them to generate the initial conditions for star clusters with masses of $\sim10^5~M_{\odot}$. We then perform a series of direct-tree hybrid $N$-body simulations to follow runaway stellar collisions in the dense star clusters. In all the cluster models except one, runaway collisions occur within a few million years, and the mass of the central, most massive star reaches $\sim400-1900~M_{\odot}$. Such very massive stars collapse to leave intermediate-mass black holes (IMBHs). The diversity of the final masses may be attributed to the differences in a few basic properties of the host halos such as mass, central gas velocity dispersion, and mean gas density of the central core. Finally, we derive the IMBH mass to cluster mass ratios, and compare them with the observed blackhole to bulge mass ratios in the present-day universe.
We utilize the HSC CAMIRA cluster catalog and the photo-$z$ galaxy catalog constructed in the HSC wide field (S16A), covering $\sim$ 174 deg$^{2}$, to study the star formation activity of galaxies in different environments over 0.2 $<$ $z$ $<$ 1.1. We probe galaxies down to $i \sim$ 26, corresponding to a stellar mass limit of log$_{10}$(M$_*$/M$_{\odot}$) $\sim$ 8.2 and $\sim$ 8.6 for star-forming and quiescent populations, respectively, at $z$ $\sim$ 0.2. The existence of the red sequence for low stellar mass galaxies in clusters suggests that the environmental quenching persists to halt the star formation in the low-mass regime. In addition, star-forming galaxies in groups or clusters are systematically biased toward lower values of specific star formation rate by 0.1 -- 0.3 dex with respect to those in the field and the offsets shows no strong redshift evolution over our redshift range, implying a universal slow quenching mechanism acting in the dense environments since $z$ $\sim$ 1.1. Moreover, the environmental quenching dominates the mass quenching in low mass galaxies, and the quenching dominance reverses in high mass ones. The transition mass is greater in clusters than in groups, indicating that the environmental quenching is more effective for massive galaxies in clusters compared to groups.
Nuclear spiral arms are small-scale transient spiral structures found in the centers of galaxies. Similarly to their galactic-scale counterparts, nuclear spiral arms exert torques on nearby objects. Within the central few hundred parsecs of a supermassive black hole (MBH), such torques affect the orbits of stars and binaries, causing orbital diffusion in energy and angular momentum. Such diffusion can drive stars and binaries to close approaches with the MBH, disrupting single stars in tidal disruption events (TDEs), or disrupting binaries, leaving a star on a tight orbit around the MBH, and an unbound star escaping the galaxy, i.e., a hypervelocity star (HVS). Here, we consider diffusion by nuclear spiral arms in the central few hundred parsecs of galactic nuclei, specifying to the Milky Way Galactic Center. We determine nuclear spiral arm-driven diffusion rates using test-particle integrations, and we compute disruption rates. Our TDE rates are up to $20\%$ higher compared to relaxation by single stars. For binaries, the enhancement is up to a factor of $\sim 100$, and our rates are roughly consistent with the observed numbers of HVSs and S-stars. Our scenario is complementary to relaxation driven by massive perturbers. In addition, our rates depend on the inclination of the binary with respect to the Galactic plane. Therefore, our scenario of diffusion by nuclear spiral arms provides an explanation for the observed anisotropic distribution of HVSs. Nuclear spiral arms may also be important for accelerating the coalescence of binary MBHs, and for supplying nuclear star clusters with stars and gas.
The Herschel Orion Protostar Survey obtained well-sampled 1.2 - 870 micron spectral energy distributions (SEDs) of over 300 protostars in the Orion molecular clouds, home to most of the young stellar objects (YSOs) in the nearest 500 pc. We plot the bolometric luminosities and temperatures for 330 Orion YSOs, 315 of which have bolometric temperatures characteristic of protostars. The histogram of bolometric temperature is roughly flat; 29% of the protostars are in Class 0. The median luminosity decreases by a factor of four with increasing bolometric temperature; consequently, the Class 0 protostars are systematically brighter than the Class I protostars, with a median luminosity of 2.3 L_sun as opposed to 0.87 L_sun. At a given bolometric temperature, the scatter in luminosities is three orders of magnitude. Using fits to the SEDs, we analyze how the luminosities corrected for inclination and foreground reddening relate to the mass in the inner 2500 AU of the best-fit model envelopes. The histogram of envelope mass is roughly flat, while the median corrected luminosity peaks at 15 L_sun for young envelopes and falls to 1.7 L_sun for late-stage protostars with remnant envelopes. The spread in luminosity at each envelope mass is three orders of magnitude. Envelope masses that decline exponentially with time explain the flat mass histogram and the decrease in luminosity, while the formation of a range of stellar masses explains the dispersion in luminosity.
We search for runaway former companions of the progenitors of nearby Galactic core-collapse supernova remnants (SNRs) in the Tycho-Gaia astrometric solution (TGAS). We look for candidates for a sample of ten SNRs with distances less than $2\;\mathrm{kpc}$, taking astrometry and $G$ magnitude from TGAS and $B,V$ magnitudes from the AAVSO Photometric All-Sky Survey (APASS). A simple method of tracking back stars and finding the closest point to the SNR centre is shown to have several failings when ranking candidates. In particular, it neglects our expectation that massive stars preferentially have massive companions. We evolve a grid of binary stars to exploit these covariances in the distribution of runaway star properties in colour - magnitude - ejection velocity space. We construct an analytic model which predicts the properties of a runaway star, in which the model parameters are the properties of the progenitor binary and the properties of the SNR. Using nested sampling we calculate the Bayesian evidence for each candidate to be the runaway and simultaneously constrain the properties of that runaway and of the SNR itself. We identify four likely runaway companions of the Cygnus Loop, HB 21, S147 and the Monoceros Loop. HD 37424 has previously been suggested as the companion of S147, however the other three stars are new candidates. The favoured companion of HB 21 is the Be star BD+50 3188 whose emission-line features could be explained by pre-supernova mass transfer from the primary. There is a small probability that the $2\;\mathrm{M}_{\odot}$ candidate runaway TYC 2688-1556-1 associated with the Cygnus Loop is a hypervelocity star. If the Monoceros Loop is related to the on-going star formation in the Mon OB2 association, the progenitor of the Monoceros Loop is required to be more massive than $40\;\mathrm{M}_{\odot}$ which is in tension with the posterior for HD 261393.
Unresolved sources of gravitational waves are at the origin of a stochastic gravitational wave background. While the computation of its mean density as a function of frequency in a homogeneous and isotropic universe is standard lore, the computation of its anisotropies requires to understand the coarse graining from local systems, to galactic scales and then to cosmology. An expression of the gravitational wave energy density valid in any general spacetime is derived. It is then specialized to a perturbed Friedmann-Lema\^itre spacetime in order to determine the angular power spectrum of this stochastic background as well as its correlation with other cosmological probes, such as the galaxy number counts and weak lensing. Our result for the angular power spectrum also provides an expression for the variance of the gravitational wave background.
Reflection Nebula NGC2023 shows specific interstellar infrared spectrum due to polycyclic aromatic hydrocarbon (PAH) in a wide wavelength range from 5 to 20 micrometer. By our previous quantum chemistry calculation, it was suggested that a molecule group having hydrocarbon pentagon-hexagon combined skeleton could reproduce ubiquitous interstellar infrared spectrum. In this paper, observed NGC2023 spectrum was compared in detail with such carrier candidates. First model molecule was di-cation (C23H12)2+ with two hydrocarbon pentagons combined with five hexagons. Observed strong infrared bands were 6.2, 7.7, 8.6, and 11.2 micrometer. Whereas, calculated strong peaks were 6.4, 7.5, 7.7, 8.5, and 11.2 micrometer. Observed weaker bands from 10 to 15 micrometer were 11.0, 12.0, 12.7, 13.5, and 14.2 micrometer, which were reproduced well by computed bands as 10.9, 12.0, 12.6, 13.6, and 14.0 micrometer. From 15 to 20 micrometer, observed 15.8, 16.4, 17.4, 17.8, and 19.0 micrometer were correlated with calculated 15.6, 16.5, 17.2, 18.2, and 18.8 micrometer. It should be noted that we could successfully reproduce interstellar infrared spectrum by applying a single molecule. Second model molecule was (C12H8)3+ with one pentagon combined with two hexagons. Again, observed strong bands at 6.2, 7.7, 8.6, 11.2 and 12.7 micrometer were successfully computed as 6.3, 7.4, 7.7, 8.6, 11.1, and 12.8 micrometer. It was concluded that by introducing hydrocarbon pentagon-hexagon combined ionized molecules, interstellar PAH oriented infrared spectrum could be successfully reproduced.
We are motivated by the recent measurements of dust opacity indices beta around young stellar objects (YSOs), which suggest that efficient grain growth may have occurred earlier than the Class I stage. The present work makes use of abundant archival interferometric observations at submillimeter,millimeter, and centimeter wavelength bands to examine grain growth signatures in the dense inner regions (<1000 AU) of nine Class 0 YSOs. A systematic data analysis is performed to derive dust temperatures, optical depths, and dust opacity indices based on single-component modified black body fittings to the spectral energy distributions (SEDs). The fitted dust opacity indices (beta) are in a wide range of 0.3 to 2.0 when single-component SED fitting is adopted. Four out of the nine observed sources show beta lower than 1.7, the typical value of the interstellar dust. Low dust opacity index (or spectral index) values may be explained by the effect of dust grain growth, which makes beta<1.7. Alternatively, the very small observed values of beta may be interpreted by the presence of deeply embedded hot inner disks, which only significantly contribute to the observed fluxes at long wavelength bands. This possibility can be tested by the higher angular resolution imaging observations of ALMA, or more detailed sampling of SEDs in the millimeter and centimeter bands. The beta values of the remaining five sources are close to or consistent with 1.7, indicating that grain growth would start to significantly reduce the values of beta no earlier than the late-Class 0 stage for these YSOs.
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