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We test the galactic outflow model by probing associated galaxies of four strong intergalactic CIV absorbers at $z=5$--6 using the Hubble Space Telescope (HST) ACS ramp narrowband filters. The four strong CIV absorbers reside at $z=5.74$, $5.52$, $4.95$, and $4.87$, with column densities ranging from $N_{\rm{CIV}}=10^{13.8}$ cm$^{-2}$ to $10^{14.8}$ cm$^{-2}$. At $z=5.74$, we detect an i-dropout Ly$\alpha$ emitter (LAE) candidate with a projected impact parameter of 42 physical kpc from the CIV absorber. This LAE candidate has a Ly$\alpha$-based star formation rate (SFR$_{\rm{Ly\alpha}}$) of 2 $M_\odot$ yr$^{-1}$ and a UV-based SFR of 4 $M_\odot$ yr$^{-1}$. Although we cannot completely rule out that this $i$-dropout emitter may be an [OII] interloper, its measured properties are consistent with the CIV powering galaxy at $z=5.74$. For CIV absorbers at $z=4.95$ and $z=4.87$, although we detect two LAE candidates with impact parameters of 160 kpc and 200 kpc, such distances are larger than that predicted from the simulations. Therefore we treat them as non-detections. For the system at $z=5.52$, we do not detect LAE candidates, placing a 3-$\sigma$ upper limit of SFR$_{\rm{Ly\alpha}}\approx 1.5\ M_\odot$ yr$^{-1}$. In summary, in these four cases, we only detect one plausible CIV source at $z=5.74$. Combining the modest SFR of the one detection and the three non-detections, our HST observations strongly support that smaller galaxies (SFR$_{\rm{Ly\alpha}} \lesssim 2\ M_\odot$ yr$^{-1}$) are main sources of intergalactic CIV absorbers, and such small galaxies play a major role in the metal enrichment of the intergalactic medium at $z\gtrsim5$.
NGC 3115 is the nearest galaxy hosting a billion solar mass black hole and is also a low-luminosity active galactic nucleus (LLAGN). X-ray observations of this LLAGN are able to spatially resolve the hot gas within the sphere of gravitational influence of the supermassive black hole. These observations make NGC 3115 an important testbed for black hole accretion theory in galactic nuclei since they constrain the outer boundary conditions of the hot accretion flow. We present a compilation of the multiwavelength spectral energy distribution (SED) of the nucleus of NGC 3115 from radio to X-rays. We report the results from modeling the observed SED with RIAF radiative models. The radio emission can be well-explained by synchrotron emission from the RIAF without the need for contribution from a relativistic jet. We obtain a tight constraint on the RIAF density profile, $\rho(r) \propto r^{-0.73 \pm 0.02}$, implying that mass-loss through subrelativistic outflows from the RIAF is significant. The lower frequency radio observation requires the synchrotron emission from a nonthermal electron population in the RIAF, similarly to Sgr A*.
Methyl isocyanate (CH3NCO) is one of the important complex organic molecules detected on the comet 67P/Churyumov-Gerasimenko by Rosetta's Philae lander. It was also detected in hot cores around high-mass protostars along with a recent detection in the solar-type protostar IRAS 16293-2422. We propose here a gas-grain chemical model to form CH3NCO after reviewing various formation pathways with quantum chemical computations. We have used NAUTILUS 3-phase gas-grain chemical model to compare observed abundances in the IRAS 16293-2422. Our chemical model clearly indicates the ice phase origin of CH3NCO.
We present the first HI spectral line images of the nearby, star-forming dwarf galaxies UGC11411 and UGC 8245, acquired as part of the "Observing for University Classes" program with the Karl G. Jansky Very Large Array (VLA). These low-resolution images localize the HI gas and reveal the bulk kinematics of each system. Comparing with HST broadband and ground-based H{\alpha} imaging, we find that the ongoing star formation in each galaxy is associated with the highest HI mass surface density regions. UGC 8245 has a much lower current star formation rate than UGC 11411, which harbors very high surface brightness H{\alpha} emission in the inner disk and diffuse, lower surface brightness nebular gas that extends well beyond the stellar disk as traced by HST. We measure the dynamical masses of each galaxy and find that the halo of UGC 11411 is more than an order of magnitude more massive than the halo of UGC 8245, even though the HI and stellar masses of the sources are similar. We show that UGC8245 shares similar physical properties with other well-studied low-mass galaxies, while UGC11411 is more highly dark matter dominated. Both systems have negative peculiar velocities that are associated with a coherent flow of nearby galaxies at high supergalactic latitude.
We report the detection of widespread CH$_2$OHCHO and HOCH$_2$CH$_2$OH emission in Galactic center giant molecular cloud Sagittarius B2 using the Shanghai Tianma 65m Radio Telescope. Our observations show for the first time that the spatial distribution of these two important prebiotic molecules extends over 15 arc-minutes, corresponding to a linear size of approximately 36 pc. These two molecules are not just distributed in or near the hot cores. The abundance of these two molecules seems to decrease from the cold outer region to the central region associated with star-formation activity. Results present here suggest that these two molecules are likely to form through a low temperature process. Recent theoretical and experimental studies demonstrated that prebiotic molecules can be efficiently formed in icy grain mantles through several pathways. However, these complex ice features cannot be directly observed, and most constraints on the ice compositions come from millimeter observations of desorbed ice chemistry products. These results, combined with laboratory studies, strongly support the existence of abundant prebiotic molecules in ices.
The environmental dependence of the morphology of dwarf galaxies in isolated satellite systems is analyzed to understand the origin of the dwarf galaxy morphology using the visually classified morphological types of 5836 local galaxies with $z \lesssim 0.01$. We consider six sub-types of dwarf galaxies, dS0, dE, dE$_{bc}$, dSph, dE$_{blue}$, and dI, of which the first four sub-types are considered as early-type and the last two as late-type. The environmental parameters we consider are the projected distance from the host galaxy ($r_{p}$), local and global background densities, and the host morphology. The spatial distributions of dwarf satellites of early-type galaxies are much different from those of dwarf satellites of late-type galaxies, suggesting the host morphology combined with $r_{p}$ plays a decisive role on the morphology of the dwarf satellite galaxies. The local and global background densities play no significant role on the morphology of dwarfs in the satellite systems hosted by early-type galaxies. However, in the satellite system hosted by late-type galaxies, the global background densities of dE and dSph satellites are significantly different from those of dE$_{bc}$, dE$_{blue}$, and dI satellites. The blue-cored dwarf satellites (dE$_{bc}$) of early-type galaxies are likely to be located at $r_{p} > 0.3$ Mpc to keep their cold gas from the ram pressure stripping by the hot corona of early-type galaxies. The spatial distribution of dE$_{bc}$ satellites of early-type galaxies and their global background densities suggest that their cold gas is intergalactic material accreted before they fall into the satellite systems.
(Abridged) On small scales, there exists a tension between observations of dwarf galaxies and predictions for low-mass dark matter halos from simulations (often referred to as the small scale crisis). Detailed observations of low mass galaxies are critical for constraining the baryonic feedback processes that are used to alleviate these discrepancies. Dwarf galaxies with a substantial reservoir of neutral hydrogen (HI) are likely to be isolated, helping to disentangle intrinsic properties from evolutionary effects, and HI kinematics offer an immediate constraint on the hosting dark matter halo. Given MeerKAT's exquisite sensitivity, it can potentially contribute to these studies of low-mass HI-rich dwarf galaxies that will help resolve the small scale crisis. The current large HI surveys are not designed for these studies, but will still manage to detect a sample of galaxies with HI masses below 10^7 Msun comparable to the number of systems currently in the literature, and will resolve ~15 systems with masses below 10^8.5 Msun, a critical regime for addressing which dark matter halos host low-mass galaxies. We propose a thousand hour survey of the Centaurus region, encompassing the M83 and CenA galaxy groups, which can robustly address the central question: "How many galaxies equivalent to Leo T are there in the Centaurus region?" Leo T is the lowest mass, gas-rich galaxy currently known; our proposed survey is designed to be able to detect an object of similar HI mass and linewidth throughout the volume of the Centuaurus region, which will provide a full census of how many objects like this there are in a typical galaxy group. In addition, planes of satellites have recently been identified around CenA and our survey will be able to address how far out these planes extend: are they structures concentrated only around the central galaxy or are they connected to large scale structure?
Nuclear activity and star formation play relevant roles in the early stages of galaxy formation. We aim at identifying them in high redshift galaxies by exploiting high-resolution and sensitivity X-ray and mm data to confirm their presence and relative role in contributing to the galaxy SEDs and energy budget. We present the data, model and analysis in the X-ray and mm bands for two strongly lensed galaxies, SDP.9 and SDP.11, selected in the Herschel-ATLAS catalogues as having an excess emission in the mid-IR regime at z>1.5, suggesting nuclear activity in the early stages of galaxy formation. We observed both of them in X-ray with Chandra and analyzed the high-resolution mm data available in the ALMA Science Archive for SDP9, and, by combining the information available, we reconstructed the source morphology. Both the targets were detected in the X-ray, strongly indicating the presence of highly obscured nuclear activity. High resolution ALMA observations for SDP9 in continuum and CO(6-5) spectral line allowed us to estimate the lensed galaxy redshift to a better accuracy than pre-ALMA estimates and to model the emission of the optical, mm, and X-ray band emission for this galaxy. We demonstrated that the X-ray emission is generated in the nuclear environment and it strongly support the presence of nuclear activity in this object. Hence, we identified weak nuclear activity associated with high-z galaxies with large star formation rates, useful to extend the investigation of the relationship between star formation and nuclear activity to two intrinsically less luminous, high-z star forming galaxies than was possible so far. Given our results only for two objects, they solely cannot constrain the evolutionary models, but provide us with interesting hints and set an observational path towards addressing the role of star formation and nuclear activity in forming galaxies.
The early evolution during massive star cluster formation is still uncertain. Observing embedded clusters at their earliest stages of formation can provide insight into the spatial and temporal distribution of the stars and thus probe different star cluster formation models. We present near-infrared imaging of an 8'*13'(5.4pc*8.7pc) region around the massive infalling clump G286.21+0.17(also known as BYF73). The stellar content across the field is determined and photometry is derived in order to { obtain} stellar parameters for the cluster members. We find evidence for some sub-structure (on scales less than a pc diameter) within the region with apparently at least three different sub-clusters associated with the molecular clump based on differences in extinction and disk fractions. At the center of the clump we identify a deeply embedded sub-cluster. Near-infrared excess is detected for 39-44% in the two sub-clusters associated with molecular material and 27% for the exposed cluster. Using the disk excess as a proxy for age this suggests the clusters are very young. The current total stellar mass is estimated to be at least 200 Msun. The molecular core hosts a rich population of pre-main sequence stars. There is evidence for multiple events of star formation both in terms of the spatial distribution within the star forming region and possibly from the disk frequency.
Due to its accuracy and generality, Monte Carlo radiative transfer (MCRT) has emerged as the prevalent method for Ly$\alpha$ radiative transfer in arbitrary geometries. The standard MCRT encounters a significant efficiency barrier in the high optical depth, diffusion regime. Multiple acceleration schemes have been developed to improve the efficiency of MCRT but the noise from photon packet discretization remains a challenge. The discrete diffusion Monte Carlo (DDMC) scheme has been successfully applied in state-of-the-art radiation hydrodynamics (RHD) simulations. Still, the established framework is not optimal for resonant line transfer. Inspired by the DDMC paradigm, we present a novel extension to resonant DDMC in which diffusion in space and frequency are treated on equal footing. We explore the robustness of our new method and demonstrate a level of performance that justifies incorporating the method into existing Ly$\alpha$ codes. We present computational speedups of $\sim 10^2$-$10^6$ relative to contemporary MCRT implementations with aggressive core-skipping. This is because the resonant DDMC runtime scales with the spatial and frequency resolution rather than the number of scatterings - the latter is typically $\propto \tau_0$ for static media, or $\propto (a \tau_0)^{2/3}$ with core-skipping. We anticipate new frontiers in which on-the-fly Ly$\alpha$ radiative transfer calculations are feasible in 3D RHD. More generally, resonant DDMC is transferable to any computationally demanding problem amenable to a Fokker-Planck approximation of frequency redistribution.
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We study the morphologies and sizes of galaxies at z>5 using high-resolution cosmological zoom-in simulations from the Feedback In Realistic Environments project. The galaxies show a variety of morphologies, from compact to clumpy to irregular. The simulated galaxies have more extended morphologies and larger sizes when measured using rest-frame optical B-band light than rest-frame UV light; sizes measured from stellar mass surface density are even larger. The UV morphologies are usually dominated by several small, bright young stellar clumps that are not always associated with significant stellar mass. The B-band light traces stellar mass better than the UV, but it can also be biased by the bright clumps. At all redshifts, galaxy size correlates with stellar mass/luminosity with large scatter. The half-light radii range from 0.01 to 0.2 arcsec (0.05-1 kpc physical) at fixed magnitude. At z>5, the size of galaxies at fixed stellar mass/luminosity evolves as (1+z)^{-m}, with m~1-2. For galaxies less massive than M_star~10^8 M_sun, the ratio of the half-mass radius to the halo virial radius is ~10% and does not evolve significantly at z=5-10; this ratio is typically 1-5% for more massive galaxies. A galaxy's "observed" size decreases dramatically at shallower surface brightness limits. This effect may account for the extremely small sizes of z>5 galaxies measured in the Hubble Frontier Fields. We provide predictions for the cumulative light distribution as a function of surface brightness for typical galaxies at z=6.
We present the results of two-component (disc+bar) and three-component (disc+bar+bulge) multiwavelength 2D photometric decompositions of barred galaxies in five SDSS bands ($ugriz$). This sample of $\sim$3,500 nearby ($z<0.06$) galaxies with strong bars selected from the Galaxy Zoo citizen science project is the largest sample of barred galaxies to be studied using photometric decompositions which include a bar component. With detailed structural analysis we obtain physical quantities such as the bar- and bulge-to-total luminosity ratios, effective radii, S\'ersic indices and colours of the individual components. We observe a clear difference in the colours of the components, the discs being bluer than the bars and bulges. An overwhelming fraction of bulge components have S\'ersic indices consistent with being pseudobulges. By comparing the barred galaxies with a mass-matched and volume-limited sample of unbarred galaxies, we examine the connection between the presence of a large-scale galactic bar and the properties of discs and bulges. We find that the discs of unbarred galaxies are significantly bluer compared to the discs of barred galaxies, while there is no significant difference in the colours of the bulges. We find possible evidence of secular evolution via bars that leads to the build-up of pseudobulges and to the quenching of star formation in the discs. We identify a subsample of unbarred galaxies with an inner lens/oval and find that their properties are similar to barred galaxies, consistent with an evolutionary scenario in which bars dissolve into lenses. This scenario deserves further investigation through both theoretical and observational work.
We present the variability and time lag measurements of PG 0934+013 based on a photometric and spectroscopic monitoring campaign over a two year period. We obtained 46 epochs of data from the spectroscopic campaign, which was carried out using the Southern African Large Telescope with $\sim$1 week cadence over two sets of 4 month-long observing period, while we obtained 80 epochs of \textit{B}-band imaging data using a few 1-m class telescopes. Due to the seven month gap between the two observing periods, we separately measured the time lags of broad emission lines including H$\beta$, by comparing the emission line light curve with the \textit{B}-band continuum light curve using the cross-correlation function techniques. We determined the H$\beta$ lag, $\tau_{\rm cent} = 8.46^{+2.08}_{-2.14}$ days in the observed-frame based on Year 2 data, while the time lag from Year 1 data was not reliably determined. Using the rms spectrum of Year 2 data, we measured the \Hb\ line dispersion \sigmaline = 668 $\pm$ 44 \kms\ after correcting for the spectral resolution. Adopting a virial factor f = 4.47 from Woo et al. 2015, we determined the black hole mass M$_{BH}$ = $3.13 ^{+0.91} _{-0.93} \times 10^{6}$ \msun based on the \Hb\ time lag and velocity.
We explore the multiphase structure of the circumgalactic medium (CGM) probed by synthetic spectra through a cosmological zoom-in galaxy formation simulation. We employ a Bayesian method for modeling a combination of absorption lines to derive physical properties of absorbers regardless of the signal-to-noise or whether a particular line is actually detected. This allows us to treat detections (including saturated systems) and non-detections in a uniform manner. We find that in the lines of sight passing through localized density structures, absorption lines of low, intermediate and high ions are present in the spectrum and overlap in velocity space. To our surprise, all of the ions can be combined to derive the line of sight (LOS) mass-weighted properties, although the ions are not co-spatial. In lines of sight that go through the hot halo, only HI and high ions are present. In such lines of sight, the absorption lines are typically broad due to the complex velocity fields across the entire halo. We show that the derived gas density, temperature, and metallicity match closely the corresponding HI mass-weighted averages along the LOS. We also show that constraints on HI and OVI together with upper limits on NV and/or NeVIII, can in principle provide constraints on the properties of the hot halo itself.
[Abridged] Typical disc galaxies forming in a LambdaCDM cosmology encounter a violent environment, where they often experience mergers with massive satellites. The fact that disc galaxies are ubiquitous in the local Universe suggests that a quiescent history is not necessary for their formation. Modern cosmological simulations can now obtain relatively realistic populations of disc galaxies, but it still remains to be clarified how discs manage to survive massive mergers. Here we use a suite of high-resolution hydrodynamical simulations set in a LambdaCDM cosmology to elucidate the fate of discs encountering massive mergers. We extract a sample of approximately 100 disc galaxies and follow the changes in their post-merger morphologies, as tracked by their disc-to-total ratios (D/T). We also examine the relations between their present-day morphology, assembly history and gas fractions. We find that approximately half of present-day disc galaxies underwent at least one merger with a satellite of total mass exceeding the host system's stellar mass, a third had mergers with satellites of mass exceeding 3 times the host's stellar mass, and approximately one-sixth had mergers with satellites of mass exceeding 10 times of the host's stellar mass. These mergers lead to a sharp, but often temporary, decrease in the D/T of the hosts, implying that discs are usually disrupted but then quickly re-grow. To do so, high cold gas fractions are required post-merger, as well as a relatively quiescent recent history (over a few Gyrs before z=0). Our results show that discs can form via diverse merger pathways and that quiescent histories are not the dominant mode of disc formation.
The fundamental 28SiH+ ion has been characterized in a collaborative work, utilizing a hollow-cathode-discharge laser-spectrometer and a cryogenic ion trap spectrometer. Twenty-three vibration-rotation transitions around 4.75 um have been detected with high accuracy. This has facilitated the first direct measurement of the pure rotational transition J=1<-0 at 453056.3632(4) MHz in the trap spectrometer. The measured and accurately predicted transitions enable the search for this ion in space with IR and sub-mm telescopes.
We report Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet and Arecibo Telescope H{\sc i} 21cm spectroscopic studies of six damped and sub-damped Lyman-$\alpha$ absorbers (DLAs and sub-DLAs, respectively) at $z \lesssim 0.1$, that have yielded estimates of their H{\sc i} column density, metallicity and atomic gas mass. This significantly increases the number of DLAs with gas mass estimates, allowing the first comparison between the gas masses of DLAs and local galaxies. Including three absorbers from the literature, we obtain H{\sc i} masses $\approx (0.24 - 5.2) \times 10^9 \: {\rm M}_\odot$, lower than the knee of the local H{\sc i} mass function. This implies that massive galaxies do not dominate the absorption cross-section for low-$z$ DLAs. We use Sloan Digital Sky Survey photometry and spectroscopy to identify the likely hosts of four absorbers, obtaining low stellar masses, $\approx 10^7-10^{8.7} M_\odot$, in all cases, consistent with the hosts being dwarf galaxies. We obtain high H{\sc i} 21\,cm or CO emission line widths, $\Delta V_{20} \approx 100-290$~km~s$^{-1}$, and high gas fractions, $f_{\rm HI} \approx 5-100$, suggesting that the absorber hosts are gas-rich galaxies with low star formation efficiencies. However, the H{\sc i} 21\,cm velocity spreads ($\gtrsim 100$~km~s$^{-1}$) appear systematically larger than the velocity spreads in typical dwarf galaxies.
We report the first detections of associated H{\sc i} 21\,cm absorption in Gigahertz-peaked-spectrum (GPS) sources at high redshifts, $z > 1$, using the Giant Metrewave Radio Telescope (GMRT). Our GMRT search for associated H{\sc i} 21\,cm absorption in a sample of 12 GPS sources yielded two new detections of absorption, towards TXS~1200+045 at $z = 1.226$ and TXS~1245$-$197 at $z = 1.275$, and five non-detections. These are only the sixth and seventh detections of associated H{\sc i} 21\,cm absorption in active galactic nuclei (AGNs) at $z > 1$. Both H{\sc i} 21\,cm absorption profiles are wide, with velocity spans between nulls of $\approx 600$~km~s$^{-1}$ (TXS~1200+045) and $\approx 1100$~km~s$^{-1}$ (TXS~1245$-$197). In both absorbers, the large velocity spread of the absorption and its blueshift from the AGN, suggests that it arises in outflowing neutral gas, perhaps driven by the radio jets to high velocities. We derive mass outflow rates of ${\dot M} \approx 32 \; {\rm M}_\odot$~yr$^{-1}$ (TXS~1200+045) and ${\dot M} \approx 18 \; {\rm M}_\odot$~yr$^{-1}$ (TXS~1245$-$197), comparable to the mass outflow rates seen earlier in low-redshift active galactic nuclei.
Within the early Universe, `extreme' star formation may have been the norm rather than the exception. Super Star Clusters (SSCs; $M_\star$ $\gtrsim$ 10$^5$ M$_\odot$) are thought to be the modern-day analogs of globular clusters, relics of a cosmic time ($z$ $\gtrsim$ 2) when the Universe was filled with vigorously star-forming systems. The giant HII region 30 Doradus in the Large Magellanic Cloud (LMC) is often regarded as a benchmark for studies of extreme star formation. Here, we report the discovery of a massive embedded star forming complex spanning $\sim$ 500 pc in the unexplored southwest region of the LMC, which manifests itself as a younger, embedded twin of 30 Doradus. Previously known as N79, this region has a star formation efficiency exceeding that of 30 Doradus by a factor of $\sim$ 2 as measured over the past $\lesssim$ 0.5 Myr. Moreover, at the heart of N79 lies the most luminous infrared (IR) compact source discovered with large-scale IR surveys of the LMC and Milky Way, possibly a precursor to the central SSC of 30 Doradus, R136. The discovery of a nearby candidate SSC may provide invaluable information to understand how extreme star formation proceeds in the current and high-redshift Universe.
Abundance anomalies in globular clusters provide strong evidence for multiple stellar populations within each cluster. These populations are usually interpreted as distinct generations, with the currently observed second-generation stars having formed in part from the ejecta of massive, first-generation "polluter" stars, giving rise to the anomalous abundance patterns. The precise nature of the polluters and their enrichment mechanism are still unclear. Even so, the chemical abundances measured in second-generation stars within the globular cluster NGC 2419 provide insight into this puzzling process. Previous work used Monte Carlo nuclear reaction network calculations to constrain the temperature-density conditions that could reproduce the observed abundances, thereby placing robust limits on the origins of the polluter material. The effect of individual reaction rates on these conditions has not been studied, however. Thus, we perform an exhaustive sensitivity study on the nuclear physics input to determine which reactions have the greatest impact on these predictions. We find that the $^{30}$Si(p,$\gamma$)$^{31}$P, $^{37}$Ar(p,$\gamma$)$^{38}$K, $^{38}$Ar(p,$\gamma$)$^{39}$K, and $^{39}$K(p,$\gamma$)$^{40}$Ca reactions are all critical in determining the temperature-density conditions, and ultimately, the origin of the polluter material. We conclude with recommendations for future experiments.
We analyzed high angular resolution observations of the Very Large Array archive at a wavelength of 7 mm of the L1551 IRS 5 binary system. Six sets of observations,five with the A configuration and one with the B configuration, were used, covering a time span of about 15 years. With these multi-epoch data, we estimated the absolute and relative proper motions of the binary system, which are about 25.1 mas/yr (~ 16.7 km/s considering a distance of 140 pc) and 4.2 mas/yr, respectively. Finally, based on the relative proper motion, we estimated a total mass of the L1551 IRS 5 binary system of 1.7 Msun and an orbital period of 246 years.
Fast Radio Bursts (FRBs), characterized by strong bursts of radiation intensity at radio wavelengths lasting on the order of a millisecond, have yet to be firmly associated with a family, or families, of astronomical sources. It follows that despite the large number of proposed models no well-defined physical process has been identified to explain this phenomenon. In this paper, we demonstrate how Dicke's superradiance, for which evidence has recently been found in the interstellar medium, can account for the characteristics associated to FRBs. Our analysis and modelling of previously detected FRBs suggest they could originate from regions in many ways similar to those known to harbor masers or megamasers, and result from the coherent radiation emanating from populations of molecules associated with large-scale entangled quantum mechanical states. We estimate this entanglement to involve as many as ~10^(30) to ~10^(32) molecules over distances spanning 100 to 1000 AU.
We investigate the upper stellar mass limit set by radiative feedback by the forming star with various accretion rates and metallicities. To this end, we numerically solve the structures of both a protostar and its surrounding accretion envelope assuming a spherical symmetric and steady flow. The optical depth of the dust cocoon, a dusty part of the accretion envelope, differs among the direct light from the stellar photosphere and the diffuse light re-emitted as dust thermal emission. As a result, varying the metallicity qualitatively changes the way that the radiative feedback suppresses the accretion flow. With a fixed accretion rate of $10^{-3}M_{\odot} {\rm yr^{-1}}$, the both direct and diffuse lights jointly operate to prevent the mass accretion at $Z \gtrsim 10^{-1}Z_{\odot}$. At $Z \lesssim 10^{-1}Z_{\odot}$, the diffuse light is no longer effective, and the direct light solely limits the mass accretion. At $Z \lesssim 10^{-3}Z_{\odot}$, the HII region formation plays an important role in terminating the accretion. The resultant upper mass limit increases with decreasing metallicity, from a few $\times~10~M_\odot$ to $\sim 10^3~M_\odot$ over $Z = 1Z_{\odot} - 10^{-4}~Z_\odot$. We also illustrate how the radiation spectrum of massive star-forming cores changes with decreasing metallicity. First, the peak wavelength of the spectrum, which is located around $30 \mu {\rm m}$ at $1Z_{\odot}$, shifts to $< 3 \mu {\rm m}$ at $Z \lesssim 0.1 Z_\odot$. Second, a characteristic feature at $10 \mu \rm{m}$ due to the amorphous silicate band appears as a dip at $1Z_{\odot}$, but changes to a bump at $Z \lesssim 0.1 Z_{\odot}$. Using these spectral signatures, we can search massive accreting protostars in nearby low-metallicity environments with up-coming observations.
We decompose the Lyman-{\alpha} (Ly{\alpha}) forest of an extensive sample of 74 high signal-to-noise ratio and high-resolution quasar spectra into a collection of Voigt profiles. Absorbers located near caustics in the peculiar velocity field have the smallest Doppler parameters, resulting in a low-$b$ cutoff in the $b$-$N_{\text{HI}}$ set by the thermal state of intergalactic medium (IGM). We fit this cutoff as a function of redshift over the range $2.0\leq z \leq 3.4$, which allows us to measure the evolution of the IGM temperature-density ($T= T_0 (\rho/ \rho_0)^{\gamma-1}$) relation parameters $T_0$ and $\gamma$. We calibrate our measurements against Ly$\alpha$ forest simulations, using 21 different thermal models of the IGM at each redshift, also allowing for different values of the IGM pressure smoothing scale. We adopt a forward-modeling approach and self-consistently apply the same algorithms to both data and simulations, propagating both statistical and modeling uncertainties via Monte Carlo. The redshift evolution of $T_0$ shows a suggestive peak at $z=2.8$, while our evolution of $\gamma$ is consistent with $\gamma\simeq 1.4$ and disfavors inverted temperature-density relations. Our measured evolution of $T_0$ and $\gamma$ are generally in good agreement with previous determinations in the literature. Both the peak in the evolution of $T_0$ at $z = 2.8$, as well as the high temperatures $T_0\simeq 15000-20000\,$K that we observe at $2.4 < z < 3.4$, strongly suggest that a significant episode of heating occurred after the end of HI reionization, which was most likely the cosmic reionization of HeII.
We present spatially resolved ALMA images of CO J=3-2 emission from the protoplanetary disk around HD100546. We model the spatially-resolved kinematic structure of the CO emission. Assuming a velocity profile which prescribes a flat or flared emitting surface in Keplerian rotation, we uncover significant residuals with a peak of $\approx7\delta v$, where $\delta v = 0.21$ km s$^{-1}$ is the width of a spectral resolution element. The residuals reveal the possible presence of a severely warped and twisted inner disk extending to at most 100au. Adapting the model to include a misaligned inner gas disk with (i) an inclination almost edge-on to the line of sight, and (ii) a position angle almost orthogonal to that of the outer disk reduces the residuals to $< 3\delta v$. However, these findings are contrasted by recent VLT/SPHERE, MagAO/GPI, and VLTI/PIONIER observations of HD100546 that show no evidence of a severely misaligned inner dust disk down to spatial scales of $\sim 1$au. An alternative explanation for the observed kinematics are fast radial flows mediated by (proto)planets. Inclusion of a radial velocity component at close to free-fall speeds and inwards of $\approx 50$au results in residuals of $\approx 4 \delta v$. Hence, the model including a radial velocity component only does not reproduce the data as well as that including a twisted and misaligned inner gas disk. Molecular emission data at a higher spatial resolution (of order 10au) are required to further constrain the kinematics within $\lesssim 100$au. HD100546 joins several other protoplanetary disks for which high spectral resolution molecular emission shows that the gas velocity structure cannot be described by a purely Keplerian velocity profile with a universal inclination and position angle. Regardless of the process, the most likely cause is the presence of an unseen planetary companion. (Abridged)
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The spiral structure of the Milky Way can be simulated by adopting percolation theory, where the active zones are produced by the evolution of many supernova (SN). Here we assume conversely that the percolative process is triggered by superbubbles (SB), the result of multiple SNs. A first thermal model takes into account a bursting phase which evolves in a medium with constant density, and a subsequent adiabatic expansion which evolves in a medium with decreasing density along the galactic height. A second cold model follows the evolution of an SB in an auto-gravitating medium in the framework of the momentum conservation in a thin layer. Both the thermal and cold models are compared with the results of numerical hydro-dynamics. A simulation of GW~46.4+5.5, the Gould Belt, and the Galactic Plane is reported. An elementary theory of the image, which allows reproducing the hole visible at the center of the observed SB, is provided.
Cold ($T\sim 10^{4} \ \mathrm{K}$) gas is very commonly found in both galactic and cluster halos. There is no clear consensus on its origin. Such gas could be uplifted from the central galaxy by galactic or AGN winds. Alternatively, it could form in situ by thermal instability. Fragmentation into a multi-phase medium has previously been shown in hydrodynamic simulations to take place once $t_\mathrm{cool}/t_\mathrm{ff}$, the ratio of the cooling time to the free-fall time, falls below a threshold value. Here, we use 3D plane-parallel MHD simulations to investigate the influence of magnetic fields. We find that because magnetic tension suppresses buoyant oscillations of condensing gas, it destabilizes all scales below $l_\mathrm{A}^\mathrm{cool} \sim v_\mathrm{A} t_\mathrm{cool}$, enhancing thermal instability. This effect is surprisingly independent of magnetic field orientation or cooling curve shape, and sets in even at very low magnetic field strengths. Magnetic fields critically modify both the amplitude and morphology of thermal instability, with $\delta \rho/\rho \propto \beta^{-1/2}$, where $\beta$ is the ratio of thermal to magnetic pressure. In galactic halos, magnetic fields can render gas throughout the entire halo thermally unstable, and may be an attractive explanation for the ubiquity of cold gas, even in the halos of passive, quenched galaxies.
We present the discovery of an active galactic nucleus (AGN) that is turning off and then on again in the z=0.06 galaxy SDSS J1354+1327. This episodic nuclear activity is the result of discrete accretion events, which could have been triggered by a past interaction with the companion galaxy that is currently located 12.5 kpc away. We originally targeted SDSS J1354+1327 because its Sloan Digital Sky Survey spectrum has narrow AGN emission lines that exhibit a velocity offset of 69 km s$^{-1}$ relative to systemic. To determine the nature of the galaxy and its velocity-offset emission lines, we observed SDSS J1354+1327 with Chandra/ACIS, Hubble Space Telescope/Wide Field Camera 3, Apache Point Observatory optical longslit spectroscopy, and Keck/OSIRIS integral-field spectroscopy. We find a ~10 kpc cone of photoionized gas south of the galaxy center and a ~1 kpc semi-spherical front of shocked gas, which is responsible for the velocity offset in the emission lines, north of the galaxy center. We interpret these two outflows as the result of two separate AGN accretion events; the first AGN outburst created the southern outflow, and then $<10^5$ yrs later the second AGN outburst launched the northern shock front. SDSS J1354+1327 is the galaxy with the strongest evidence for an AGN that has turned off and then on again, and it fits into the broader context of AGN flickering that includes observations of AGN light echoes.
We analyze the properties of a multiply-imaged Lyman-alpha (Lya) emitter at z=5.75 identified through SHARDS Frontier Fields intermediate-band imaging of the Hubble Frontier Fields (HFF) cluster Abell 370. The source, A370-L57, has low intrinsic luminosity (M_UV~-16.5), steep UV spectral index (\beta=-2.4+/-0.1), and extreme rest-frame equivalent width of Lya (EW(Lya)=420+180-120 \AA). Two different gravitational lens models predict high magnification (\mu~10--16) for the two detected counter-images, separated by 7", while a predicted third counter-image (\mu~3--4) is undetected. We find differences of ~50% in magnification between the two lens models, quantifying our current systematic uncertainties. Integral field spectroscopy of A370-L57 with MUSE shows a narrow (FWHM=204+/-10 km/s) and asymmetric Lya profile with an integrated luminosity L(Lya)~10^42 erg/s. The morphology in the HST bands comprises a compact clump (r_e<100 pc) that dominates the Lya and continuum emission and several fainter clumps at projected distances <1 kpc that coincide with an extension of the Lya emission in the SHARDS F823W17 and MUSE observations. The latter could be part of the same galaxy or an interacting companion. We find no evidence of contribution from AGN to the Lya emission. Fitting of the spectral energy distribution with stellar population models favors a very young (t<10 Myr), low mass (M*~10^6.5 Msun), and metal poor (Z<4x10^-3) stellar population. Its modest star formation rate (SFR~1.0 Msun/yr) implies high specific SFR (sSFR~2.5x10^-7 yr^-1) and SFR density (Sigma_SFR ~ 7-35 Msun/yr/kpc^2). The properties of A370-L57 make it a good representative of the population of galaxies responsible for cosmic reionization.
We apply an analytic Markov Chain Monte Carlo model to a sample of 18 AGN-driven biconical outflows that we identified from a sample of active galaxies with double-peaked narrow emission lines at z < 0.1 in the Sloan Digital Sky Survey. We find that 8/18 are best described as asymmetric bicones, 8/18 are nested bicones, and 2/18 are symmetric bicones. From the geometry and kinematics of the models, we find that these moderate-luminosity AGN outflows are large and energetic. The biconical outflows axes are randomly oriented with respect to the photometric major axis of the galaxy, implying a randomly oriented and clumpier torus to collimate the outflow, but the torus also allows some radiation to escape equatorially. We find that 16/18 (89%) outflows are energetic enough to drive a two-staged feedback process in their host galaxies. All of these outflows geometrically intersect the photometric major axis of the galaxy, and 23% of outflow host galaxies are significantly redder or have significantly lower specific star formation rates when compared to a matched sample of active galaxies.
It is now well established that globular clusters (GCs) exhibit star-to-star light-element abundance variations (known as multiple stellar populations, MPs). Such chemical anomalies have been found in (nearly) all the ancient GCs (more than 10 Gyr old) of our Galaxy and its close companions, but so far no model for the origin of MPs is able to reproduce all the relevant observations. To gain new insights into this phenomenon, we have undertaken a photometric Hubble Space Telescope survey to study clusters with masses comparable to that of old GCs, where MPs have been identified, but with significantly younger ages. Nine clusters in the Magellanic Clouds with ages between $\sim$ 1.5-11 Gyr have been targeted in this survey. We confirm the presence of multiple populations in all clusters older than 6 Gyr and we add NGC 1978 to the group of clusters for which MPs have been identified. With an age of $\sim$ 2 Gyr, NGC 1978 is the youngest cluster known to host chemical abundance spreads found to date. We do not detect evident star-to-star variations for slightly younger massive clusters ($\sim$ 1.7 Gyr), thus pointing towards an unexpected age dependence for the onset of multiple populations. This discovery suggests that the formation of MPs is not restricted to the early Universe and that GCs and young massive clusters share common formation and evolutionary processes.
Knowledge of the number density of H$\alpha$ emitting galaxies is vital for assessing the scientific impact of the Euclid and WFIRST missions. In this work we present predictions from a galaxy formation model, Galacticus, for the cumulative number counts of H$\alpha$-emitting galaxies. We couple Galacticus to three different dust attenuation methods and examine the counts using each method. A $\chi^2$ minimisation approach is used to compare the model predictions to observed galaxy counts and calibrate the dust parameters. We find that weak dust attenuation is required for the Galacticus counts to be broadly consistent with the observations, though the optimum dust parameters return large values for $\chi^2$, suggesting that further calibration of Galacticus is necessary. The model predictions are also consistent with observed estimates for the optical depth and the H$\alpha$ luminosity function. Finally we present forecasts for the redshift distributions and number counts for two Euclid-like and one WFIRST-like survey. For a Euclid-like survey with redshift range $0.9\leqslant z\leqslant 1.8$ and H$\alpha+{\rm [NII]}$ blended flux limit of $2\times 10^{-16}{\rm erg}\,{\rm s}^{-1}\,{\rm cm}^{-2}$ we predict a number density between 3900--4800 galaxies per square degree. For a WFIRST-like survey with redshift range $1\leqslant z\leqslant 2$ and blended flux limit of $1\times 10^{-16}{\rm erg}\,{\rm s}^{-1}\,{\rm cm}^{-2}$ we predict a number density between 10400--15200 galaxies per square degree.
We present an empirical parameterization of the [NII]/H$\alpha$ flux ratio as a function of stellar mass and redshift valid at 0 < z < 2.7 and 8.5 < log(M) < 11.0. This description can easily be applied to (i) simulations for modeling [NII] line emission, (ii) deblend [NII] and H$\alpha$ in current low-resolution grism and narrow-band observations to derive intrinsic H$\alpha$ fluxes, and (iii) to reliably forecast the number counts of H$\alpha$ emission line galaxies for future surveys such as those planned for Euclid and WFIRST. Our model combines the evolution of the locus on the BPT diagram measured in spectroscopic data out to z ~ 2.5 with the strong dependence of [NII]/H$\alpha$ on stellar mass and [OIII]/H$\beta$ observed in local galaxy samples. We find large variations in the [NII]/H$\alpha$ flux ratio at a fixed redshift due to its dependency on stellar mass, hence the assumption of a constant [NII] contamination fraction can lead to a significant under- or over-estimate of H$\alpha$ luminosities. Specifically, measurements of the intrinsic H$\alpha$ luminosity function derived from current low-resolution grism spectroscopy assuming a constant 29% contamination of [NII] are likely over-estimated by factors of 2-4 at log(L) > 43.0 and systematically under-estimated by ~50 at log(L) < 42.5 at redshifts z ~ 1.5. This has implications on the prediction of H-alpha emitters for Euclid and WFIRST. We also study the impact of blended H$\alpha$ and [NII] on the accuracy of measured spectroscopic redshifts.
Modern data empower observers to describe galaxies as the spatially and biographically complex objects they are. We illustrate this through case studies of four, $z\sim1.3$ systems based on deep, spatially resolved, 17-band + G102 + G141 Hubble Space Telescope grism spectrophotometry. Using full spectrum rest-UV/-optical continuum fitting, we characterize these galaxies' observed $\sim$kpc-scale structures and star formation rates (SFRs) and reconstruct their history over the age of the universe. The sample's diversity---passive to vigorously starforming; stellar masses $\log M_*/M_\odot=10.5$ to $11.2$---enables us to draw spatio-temporal inferences relevant to key areas of parameter space (Milky Way- to super-Andromeda-mass progenitors). Specifically, we find signs that bulge mass-fractions ($B/T$) and SF history shapes/spatial uniformity are linked, such that higher $B/T$s correlate with "inside-out growth" and central specific SFRs that peaked above the global average for all starforming galaxies at that epoch. Conversely, the system with the lowest $B/T$ had a flat, spatially uniform SFH with normal peak activity. Both findings are consistent with models positing a feedback-driven connection between bulge formation and the switch from rising to falling SFRs ("quenching"). While sample size forces this conclusion to remain tentative, this work provides a proof-of-concept for future efforts to refine or refute it: JWST, WFIRST, and the 30-m class telescopes will routinely produce data amenable to this and more sophisticated analyses. These samples---spanning representative mass, redshift, SFR, and environmental regimes---will be ripe for converting into thousands of sub-galactic-scale empirical windows on what individual systems actually looked like in the past, ushering in a new dialog between observation and theory.
We present new, spatially resolved, surface photometry in FUV and NUV from images obtained by the $\textit{Galaxy Evolution Explorer}$ (GALEX), and IRAC1 (3.6 $\mu$m) photometry from the $\textit{Spitzer Survey of Stellar Structure in Galaxies}$ (S$^{4}$G) (Sheth et al. 2010). We analyze the radial surface brightness profiles $\mu_{FUV}$, $\mu_{NUV}$, and $\mu_{[3.6]}$, as well as the radial profiles of (FUV $-$ NUV), (NUV $-$ [3.6]), and (FUV $-$ [3.6]) colors in 1931 nearby galaxies (z $<$ 0.01). The analysis of the 3.6 $\mu$m surface brightness profiles also allows us to separate the bulge and disk components in a quasi-automatic way, and to compare their light and color distribution with those predicted by the chemo-spectrophotometric models for the evolution of galaxy disks of Boissier & Prantzos (2000). The exponential disk component is best isolated by setting an inner radial cutoff and an upper surface brightness limit in stellar mass surface density. The best-fitting models to the measured scale length and central surface brightness values yield distributions of spin and circular velocity within a factor of two to those obtained via direct kinematic measurements. We find that at a surface brightness fainter than $\mu_{[3.6]}=20.89$ mag arcsec$^{-2}$, or below $3\times 10^{8}$ $M_{\odot}$ kpc$^{-2}$ in stellar mass surface density, the average specific star formation rate for star forming and quiescent galaxies remains relatively flat with radius. However, a large fraction of GALEX Green Valley galaxies (defined in Bouquin et al. 2015) shows a radial decrease in specific star formation rate. This behavior suggests that an outside-in damping mechanism, possibly related to environmental effects, could be testimony of an early evolution of galaxies from the blue sequence of star forming galaxies towards the red sequence of quiescent galaxies.
Star formation is a hierarchical process, forming young stellar structures of star clusters, associations, and complexes over a wide scale range. The star-forming complex in the bar region of the Large Magellanic Cloud is investigated with upper main-sequence stars observed by the VISTA Survey of the Magellanic Clouds. The upper main-sequence stars exhibit highly non-uniform distributions. Young stellar structures inside the complex are identified from the stellar density map as density enhancements of different significance levels. We find that these structures are hierarchically organized such that larger, lower-density structures contain one or several smaller, higher-density ones. They follow power-law size and mass distributions as well as a lognormal surface density distribution. All these results support a scenario of hierarchical star formation regulated by turbulence. The temporal evolution of young stellar structures is explored by using subsamples of upper main-sequence stars with different magnitude and age ranges. While the youngest subsample, with a median age of log($\tau$/yr)~=~7.2, contains most substructure, progressively older ones are less and less substructured. The oldest subsample, with a median age of log($\tau$/yr)~=~8.0, is almost indistinguishable from a uniform distribution on spatial scales of 30--300~pc, suggesting that the young stellar structures are completely dispersed on a timescale of $\sim$100~Myr. These results are consistent with the characteristics of the 30~Doradus complex and the entire Large Magellanic Cloud, suggesting no significant environmental effects. We further point out that the fractal dimension may be method-dependent for stellar samples with significant age spreads.
The study and quantification of UV photon-induced desorption of frozen molecules furthers our understanding of the chemical evolution of cold interstellar regions. Nitric oxide (NO) is an important intermediate species in both gas-phase and solid-phase chemical networks. In this work, we present quantitative measurements of the photodesorption of a pure NO ice.We used the tunable monochromatic synchrotron light of the DESIRS beamline of the SOLEIL facility near Paris to irradiate NO ices in the 6 - 13.6 eV range and measured desorption by quadrupole mass spectrometry.We find that NO photodesorption is very efficient, its yield being around 1e-2 molecule per incident photon for UV fields relevant to the diffuse and dense interstellar medium. We discuss the extrapolation of our results to an astrophysical context and we compare photodesorption of NO to previously studied molecules.
Recent studies of the nearest star-forming clouds of the Galaxy at submillimeter wavelengths with the Herschel Space Observatory have provided us with unprecedented images of the initial conditions and early phases of the star formation process. The Herschel images reveal an intricate network of filamentary structure in every interstellar cloud. These filaments all exhibit remarkably similar widths - about a tenth of a parsec - but only the densest ones contain prestellar cores, the seeds of future stars. The Herschel results favor a scenario in which interstellar filaments and prestellar cores represent two key steps in the star formation process: first turbulence stirs up the gas, giving rise to a universal web-like structure in the interstellar medium, then gravity takes over and controls the further fragmentation of filaments into prestellar cores and ultimately protostars. This scenario provides new insight into the origin of stellar masses and the star formation efficiency in the dense molecular gas of galaxies. Despite an apparent complexity, global star formation may be governed by relatively simple universal laws from filament to galactic scales.
The progenitors of astronomical transients are linked to a specific stellar population and galactic environment, and observing their host galaxies hence constrains the physical nature of the transient itself. Here, we use imaging from the Hubble Space Telescope, and spatially-resolved, medium resolution spectroscopy from the Very Large Telescope obtained with X-Shooter and MUSE to study the host of the very luminous transient ASASSN-15lh. The dominant stellar population at the transient site is old (around 1 to 2 Gyr), without signs of recent star-formation. We also detect emission from ionized gas, originating from three different, time-invariable, narrow components of collisionally-excited metal and Balmer lines. The ratios of emission lines in the Baldwin-Phillips-Terlevich diagnostic diagram indicate that the ionization source is a weak Active Galactic Nucleus with a black hole mass of $M_\bullet = 5_{-3}^{+8}\cdot10^{8} M_\odot$, derived through the $M_\bullet$-$\sigma$ relation. The narrow line components show spatial and velocity offsets on scales of 1 kpc and 500 km/s, respectively, that we explain by gas kinematics in the narrow line region. The location of the central component, which we argue is also the position of the supermassive black hole, aligns with that of the transient within an uncertainty of 170 pc. Using this positional coincidence as well as other similarities with the hosts of Tidal Disruption Events, we strengthen the argument that the transient emission observed as ASASSN-15lh is related to the disruption of a star around a supermassive black hole, most probably spinning with a Kerr parameter $a_\bullet\gtrsim0.5$.
Massive large-scale AGN outflows are an important element of galaxy evolution, being a way through which the AGN can affect most of the host galaxy. However, outflows evolve on timescales much longer than typical AGN episode durations, therefore most AGN outflows are not observed simultaneously with the AGN episode that inflated them. It is therefore remarkable that rather tight correlations between outflow prop- erties and AGN luminosity exist. In this paper, I show that such correlations can be preserved during the fading phase of the AGN episode, provided that the AGN lumi- nosity evolves as a power law with exponent $\alpha_{\rm d} \sim 1$ at late times. I also show that subsequent AGN episodes that illuminate an ongoing outflow are unlikely to produce outflow momentum or energy rates rising above the observed correlations. However, there may be many difficult-to-detect outflows with momentum and energy rates lower than expected from the current AGN luminosity. Detailed observations of AGN out- flow properties might help constrain the activity histories of typical and/or individual AGN.
The active galactic nuclei (AGN) lobe radio luminosities modelled in hydrodynamical simulations and most analytical models do not address the redistribution of the electron energies due to adiabatic expansion, synchrotron radiation and inverse-Compton scattering of CMB photons. We present a synchrotron emissivity model for resolved sources which includes a full treatment of the loss mechanisms spatially across the lobe, and apply it to a dynamical radio source model with known pressure and volume expansion rates. The bulk flow and dispersion of discrete electron packets is represented by tracer fields in hydrodynamical simulations; we show that the mixing of different aged electrons strongly effects the spectrum at each point of the radio map in high-powered FR-II sources. The inclusion of this mixing leads to a factor of a few discrepancy between the spectral age measured using impulsive injection models (e.g. JP model) and the dynamical age. The observable properties of radio sources are predicted to be strongly frequency dependent: FR-II lobes are expected to appear more elongated at higher frequencies, while jetted FR-I sources appear less extended. The emerging FR0 class of radio sources, comprising gigahertz peaked and compact steep spectrum sources, can potentially be explained by a population of low-powered FR-Is. The extended emission from such sources is shown to be undetectable for objects within a few orders of magnitude of the survey detection limit and to not contribute to the curvature of the radio SED.
We present our recent results about the extended narrow-line region (ENLR) of two nearby Seyfert 2 galaxies (IC 5063 and NGC 7212) obtained by modelling the observed line profiles and spectra with composite models (photoionization+shocks) in the different regions surrounding the AGN. Then, we compare the Seyfert 2 ENLRs with the very extended one recently discovered in the narrow-line Seyfert 1 (NLS1) galaxy Mrk 783. We have found several evidences of interaction between the ISM of the galaxies and their radio jets, such as a) the contribution of shocks in ionizing the high velocity gas, b) the complex kinematics showed by the profile of the emission lines, c) the high fragmentation of matter, etc. The results suggest that the ENLR of IC 5063 have a hollow bi-conical shape, with one edge aligned to the galaxy disk, which may cause some kind of dependence on velocity of the ionization parameter. Regarding the Mrk 783 properties, it is found that the extension of the optical emission is almost twice the size of the radio one and it seems due to the AGN activity, although there is contamination by star formation around 12 arcsec from the nucleus. Diagnostic diagrams excluded the contribution of star formation in IC 5063 and NGC 7212, while the shock contribution was used to explain the spectra emitted by their high velocity gas.
The influence of magnetic fields (B-fields) in the formation and evolution of bipolar bubbles, due to the expanding ionization fronts (I-fronts) driven by the Hii regions that are formed and embedded in filamentary molecular clouds, has not been well-studied yet. In addition to the anisotropic expansion of I-fronts into a filament, B-fields are expected to introduce an additional anisotropic pressure which might favor expansion and propagation of I-fronts to form a bipolar bubble. We present results based on near-infrared polarimetric observations towards the central $\sim$8'$\times$8' area of the star-forming region RCW57A which hosts an Hii region, a filament, and a bipolar bubble. Polarization measurements of 178 reddened background stars, out of the 919 detected sources in the JHKs-bands, reveal B-fields that thread perpendicular to the filament long axis. The B-fields exhibit an hour-glass morphology that closely follows the structure of the bipolar bubble. The mean B-field strength, estimated using the Chandrasekhar-Fermi method, is 91$\pm$8 {\mu}G. B-field pressure dominates over turbulent and thermal pressures. Thermal pressure might act in the same orientation as those of B-fields to accelerate the expansion of those I-fronts. The observed morphological correspondence among the B-fields, filament, and bipolar bubble demonstrate that the B-fields are important to the cloud contraction that formed the filament, gravitational collapse and star formation in it, and in feedback processes. The latter include the formation and evolution of mid-infrared bubbles by means of B-field supported propagation and expansion of I-fronts. These may shed light on preexisting conditions favoring the formation of the massive stellar cluster in RCW57A.
We characterise the oxygen abundance radial distribution of a sample of 102 spiral galaxies observed with VLT/MUSE using the O3N2 calibrator. The high spatial resolution of the data allows us to detect 14345 HII regions with the same image quality as with photometric data, avoiding any dilution effect. We develop a new methodology to automatically fit the abundance radial profiles, finding that 55 galaxies of the sample exhibit a single negative gradient. The remaining 47 galaxies also display, as well as this negative trend, either an inner drop in the abundances (21), an outer flattening (10) or both (16), which suggests that these features are a common property of disc galaxies. The presence and depth of the inner drop depends on the stellar mass of the galaxies with the most massive systems presenting the deepest abundance drops, while there is no such dependence for the outer flattening. We find that the inner drop appears always around $\rm 0.5\,r_e$, while the position of the outer flattening varies over a wide range of galactocentric distances. Regarding the main negative gradient, we find a characteristic slope of $\alpha_{O/H} = -\,0.10\pm0.03\,\rm{dex}/r_e$. This slope is independent of the presence of bars and the density of the environment. However, when inner drops or outer flattenings are detected, slightly steeper gradients are observed. This suggests that radial motions might play an important role in shaping the abundance profiles. We define a new normalisation scale ($r_{O/H}$) for the radial profiles based on the characteristic abundance gradient, with which all the galaxies show a similar position for the inner drop ($\sim0.5\,r_{O/H}$) and the outer flattening ($\sim1.5\,r_{O/H}$).Finally, we find no significant dependence of the dispersion around the negative gradient with any galaxy property, with values compatible with the uncertainties of the derived abundances.
Quasars are galaxies hosting accreting supermassive black holes; due to their brightness, they are unique probes of the early universe. To date, only few quasars have been reported at $z > 6.5$ ($<$800 Myr after the Big Bang). In this work, we present six additional $z \gtrsim 6.5$ quasars discovered using the Pan-STARRS1 survey. We use a sample of 15 $z \gtrsim 6.5$ quasars to perform a homogeneous and comprehensive analysis of this highest-redshift quasar population. We report four main results: (1) the majority of $z\gtrsim$6.5 quasars show large blueshifts of the broad CIV 1549\AA$\,$emission line compared to the systemic redshift of the quasars, with a median value $\sim$3$\times$ higher than a quasar sample at $z\sim$1; (2) we estimate the quasars' black hole masses (M$\rm_{BH}\sim$0.3$-$5 $\times$ 10$^{9}$ M$_{\odot}$) via modeling of the MgII 2798\AA$\,$emission line and rest-frame UV continuum; we find that quasars at high redshift accrete their material (with $\langle (L_{\mathrm{bol}}/L_{\mathrm{Edd}}) \rangle = 0.39$) at a rate comparable to a luminosity-matched sample at lower$-$redshift, albeit with significant scatter ($0.4$ dex); (3) we recover no evolution of the FeII/MgII abundance ratio with cosmic time; (4) we derive near zone sizes; together with measurements for $z\sim6$ quasars from recent work, we confirm a shallow evolution of the decreasing quasar near zone sizes with redshift. Finally, we present new millimeter observations of the [CII] 158 $\mu$m emission line and underlying dust continuum from NOEMA for four quasars, and provide new accurate redshifts and [CII]/infrared luminosities estimates. The analysis presented here shows the large range of properties of the most distant quasars.
Active Galactic Nuclei (AGNs) are characterized by emission of radiation over more than 10 orders of magnitude in frequency. Therefore, the execution of extensive surveys of the sky, with different types of detectors, is providing the attractive possibility to identify and to investigate the properties of AGNs on very large statistical samples. Thanks to the large spectroscopic surveys that allow detailed investigation of many of these sources, we have the opportunity to place new constraints on the nature and evolution of AGNs and to investigate their relations with the host systems. In this contribution we present the results that can be obtained by using a new interactive catalogue that we developed to investigate the range of AGN spectral energy distributions (SEDs). We present simple SED models based on data collected in the catalogue and discuss their relations with optical spectra obtained by follow up observations. We compare our findings with the expectations based on the AGN Unification Model, and we discuss the perspectives of multi-wavelength approaches to address AGN related processes such as black hole accretion and acceleration of relativistic jets.
RR Lyr stars are ideal massless tracers that can be used to study the total mass and dark matter content of the outer halo of the Milky Way. This is because they are easy to find in the light curve databases of large stellar surveys and their distances can be determined with only knowledge of the light curve. We present here a sample of 112 RR Lyr beyond 50 kpc in the outer halo of the Milky Way, excluding the Sgr streams, for which we have obtained moderate resolution spectra with Deimos on the Keck 2 Telescope. Four of these have distances exceeding 100 kpc. These were selected from a much larger set of 447 candidate RR Lyr which were datamined using machine learning techniques applied to the light curves of variable stars in the Palomar Transient Facility database. The observed radial velocities taken at the phase of the variable corresponding to the time of observation were converted to systemic radial velocities in the Galactic standard of rest. From our sample of 112 RR Lyr we determine the radial velocity dispersion in the outer halo of the Milky Way to be ~90 km/s at 50 kpc falling to about 65 km/s near 100 kpc once a small number of major outliers are removed. With reasonable estimates of the completeness of our sample of 447 candidates and assuming a spherical halo, we find that the stellar density in the outer halo declines as the -4 power of r.
Multi-wavelength surveys covering large sky volumes are necessary to obtain an accurate census of rare objects such as high luminosity and/or high redshift active galactic nuclei (AGN). Stripe 82X is a 31.3 deg$^2$ X-ray survey with $Chandra$ and $XMM$-Newton observations overlapping the legacy Sloan Digital Sky Survey (SDSS) Stripe 82 field, which has a rich investment of multi-wavelength coverage from the ultraviolet to the radio. The wide-area nature of this survey presents new challenges for photometric redshifts for AGN compared to previous work on narrow-deep fields because it probes different populations of objects that need to be identified and represented in the library of templates. Here we present an updated X-ray plus multi-wavelength matched catalog, including $Spitzer$ counterparts, and estimated photometric redshifts for 5961 (96% of a total of 6181) X-ray sources, which have a normalized median absolute deviation, $\sigma_{\rm nmad}$ = 0.06 and an outlier fraction, $\eta$ = 13.7%. The populations found in this survey, and the template libraries used for photometric redshifts, provide important guiding principles for upcoming large-area surveys such as $eROSITA$ and 3$XMM$ (in X-ray) and the Large Synoptic Survey Telescope (LSST; optical).
Hertzsprung-Russell diagrams of star forming regions show a large luminosity spread. This is incompatible with well-defined isochrones based on classic non-accreting protostellar evolution models. Protostars do not evolve in isolation of their environment, but grow through accretion of gas. In addition, while an age can be defined for a star forming region, the ages of individual stars in the region will vary. We show how the combined effect of a protostellar age spread and time-varying protostellar accretion for individual protostars can explain the observed luminosity spread. We use a global MHD simulation including a sub-scale sink particle model of a star forming region to follow the accretion process of each star. The accretion profiles are used to compute stellar evolution models for each star, incorporating a model of how the accretion energy is distributed to the disk, radiated away at the accretion shock, or incorporated into the outer layers of the protostar. Using a modelled cluster age of 5 Myr we naturally reproduce the luminosity spread and find good agreement with observations of the Collinder 69 cluster, and the Orion Nebular Cluster. It is shown how stars in binary and multiple systems can be externally forced creating recurrent episodic accretion events. We find that in a realistic global molecular cloud model massive stars build up mass over relatively long time-scales. This leads to an important conceptual change compared to the classic picture of non-accreting stellar evolution segmented in to low-mass Hayashi tracks and high-mass Henyey tracks.
Using zoom-simulations carried out with the adaptive mesh-refinement code RAMSES with a dynamic range of up to $2^{27}\approx 1.34 \times 10^{8}$ we investigate the accretion profiles around six stars embedded in different environments inside a (40 pc)$^3$ giant molecular cloud, the role of mass infall and disc instabilities on the accretion profile, and thus on the luminosity of the forming protostar. Our results show that the environment in which the protostar is embedded determines the overall accretion profile of the protostar. Infall onto the circumstellar disc may trigger gravitational disc instabilities in the disc at distances of around ~10 to ~50 AU leading to rapid transport of angular momentum and strong accretion bursts. These bursts typically last for about ~10 to a ~100 years, consistent with typical orbital times at the location of the instability, and enhance the luminosity of the protostar. Calculations with the stellar evolution code \mesa\ show that the accretion bursts induce significant changes in the protostellar properties, such as the stellar temperature and radius. We apply the obtained protostellar properties to produce synthetic observables with RadMC and predict that accretion bursts lead to observable enhancements around 20 to 200 $\mu$m in the spectral energy distribution of Class 0 type young stellar objects.
The circumstellar ammonia (NH$_3$) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH$_3$ abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry. In this article, we characterise the spatial distribution and excitation of NH$_3$ in the O-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420 with multi-wavelength observations. We observed the 1.3-cm inversion line emission with the Very Large Array (VLA) and submillimetre rotational line emission with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel from all four targets. For IK Tau and VY CMa, we observed the rovibrational absorption lines in the $\nu_2$ band near 10.5 $\mu$m with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). We also attempted to search for the rotational transition within the $v_2=1$ state near 2 mm with the IRAM 30m Telescope towards IK Tau. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH$_3$ in these CSEs. Our modelling shows that the NH$_3$ abundance relative to molecular hydrogen is generally of the order of $10^{-7}$, which is a few times lower than previous estimates that were made without considering radiative pumping and is at least 10 times higher than that in the C-rich CSE of IRC +10216. Incidentally, we also derived a new period of IK Tau from its $V$-band light curve. NH$_3$ is again detected in very high abundance in O-rich CSEs. Its emission mainly arises from localised spatial-kinematic structures that are probably denser than the ambient gas. Circumstellar shocks in the accelerated wind may contribute to the production of NH$_3$. (Abridged abstract)
The surroundings of massive protostars constitute an accretion disc which has numerically been shown to be subject to fragmentation and responsible for luminous accretion-driven outbursts. Moreover, it is suspected to produce close binary companions which will later strongly influence the star's future evolution in the Hertzsprung-Russel diagram. We present three-dimensional gravitation-radiation-hydrodynamic numerical simulations of 100 Mo pre-stellar cores. We find that accretion discs of young massive stars violently fragment without preventing the (highly variable) accretion of gaseous clumps onto the protostars. While acquiring the characteristics of a nascent low-mass companion, some disc fragments migrate onto the central massive protostar with dynamical properties showing that its final Keplerian orbit is close enough to constitute a close massive proto-binary system, having a young high-mass and a low-mass component. We conclude on the viability of the disc fragmentation channel for the formation of such short-period binaries, and that both processes -close massive binary formation and accretion bursts- may happen at the same time. FU-Orionis-type bursts, such as observed in the young high-mass star S255IR-NIRS3, may not only indicate ongoing disc fragmentation, but also be considered as a tracer for the formation of close massive binaries - progenitors of the subsequent massive spectroscopic binaries - once the high-mass component of the system will enter the main-sequence phase of its evolution. Finally, we investigate the ALMA-observability of the disc fragments.
Gas-phase methanol was recently detected in a protoplanetary disk for the first time with ALMA. The peak abundance and distribution of methanol observed in TW Hya differed from that predicted by chemical models. Here, the chemistry of methanol gas and ice is calculated using a physical model tailored for TW Hya with the aim to contrast the results with the recent detection in this source. New pathways for the formation of larger complex molecules (e.g., ethylene glycol) are included in an updated chemical model, as well as the fragmentation of methanol ice upon photodesorption. It is found that including fragmentation upon photodesorption improves the agreement between the peak abundance reached in the chemical models with that observed in TW Hya ($\sim 10^{-11}$ with respect to \ce{H2}); however, the model predicts that the peak in emission resides a factor of $2-3$ farther out in the disk than the ALMA images. Reasons for the persistent differences in the gas-phase methanol distribution between models and the observations of TW Hya are discussed. These include the location of the ice reservoir which may coincide with the compact mm-dust disk ($\lesssim 60$~au) and sources of gas-phase methanol which have not yet been considered in models. The possibility of detecting larger molecules with ALMA is also explored. Calculations of the rotational spectra of complex molecules other than methanol using a parametric model constrained by the TW Hya observations suggest that the detection of individual emission lines of complex molecules with ALMA remains challenging. However, the signal-to-noise ratio can be enhanced via stacking of multiple transitions which have similar upper energy levels.
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By using a novel interface between the modern smoothed particle hydrodynamics code GASOLINE2 and the chemistry package KROME, we follow the hydrodynamical and chemical evolution of an isolated galaxy. In order to assess the relevance of different physical parameters and prescriptions, we constructed a suite of ten simulations, in which we vary the chemical network (primordial and metal species), how metal cooling is modelled (non-equilibrium versus equilibrium), the initial gas metallicity (from ten to hundred per cent solar), and how molecular hydrogen forms on dust. This is the first work in which metal injection from supernovae, turbulent metal diffusion, and a metal network with non-equilibrium metal cooling are self-consistently included in a galaxy simulation. We find that modelling the chemical evolution of several metal species and the corresponding non-equilibrium metal cooling has important effects on the thermodynamics of the gas, the chemical abundances, and the appearance of the galaxy: the gas is typically warmer, has a larger molecular gas mass fraction, and has a smoother disc. We also conclude that, at relatively high metallicity, the choice of molecular hydrogen formation rates on dust is not crucial. Moreover, we confirm that a higher initial metallicity produces a colder gas and a larger fraction of molecular gas, with the low-metallicity simulation best matching the observed molecular Kennicutt-Schmidt relation. Finally, our simulations agree quite well with observations which link star formation rate to metal emission lines.
We present our statistical study of near infrared (NIR) variability of X-ray selected Active Galactic Nuclei (AGN) in the COSMOS field, using UltraVISTA data. This is the largest sample of AGN light curves in YJHKs bands, making possible to have a global description of the nature of AGN for a large range of redshifts, and for different levels of obscuration. To characterize the variability properties of the sources we computed the Structure Function. Our results show that there is an anti-correlation between the Structure Function $A$ parameter (variability amplitude) and the wavelength of emission, and a weak anti-correlation between $A$ and the bolometric luminosity. We find that Broad Line (BL) AGN have a considerably larger fraction of variable sources than Narrow Line (NL) AGN, and that they have different distributions of the $A$ parameter. We find evidence that suggests that most of the low luminosity variable NL sources correspond to BL AGN, where the host galaxy could be damping the variability signal. For high luminosity variable NL, we propose that they can be examples of "True type II" AGN or BL AGN with limited spectral coverage which results in missing the Broad Line emission. We also find that the fraction of variable sources classified as unobscured in the X-ray is smaller than the fraction of variable sources unobscured in the optical range. We present evidence that this is related to the differences in the origin of the obscuration in the optical and X-ray regimes.
The DECam Plane Survey is a five-band optical and near-infrared survey of the southern Galactic plane with the Dark Energy Camera at Cerro Tololo. The survey is designed to reach past the main-sequence turn-off at the distance of the Galactic center through a reddening E(B-V) of 1.5 mag. Typical single-exposure depths are 23.7, 22.8, 22.3, 21.9, and 21.0 mag in the grizY bands, with seeing around 1 arcsecond. The footprint covers the Galactic plane with |b| < 4 degrees, 5 degrees > l > -120 degrees. The survey pipeline simultaneously solves for the positions and fluxes of tens of thousands of sources in each image, delivering positions and fluxes of roughly two billion stars with better than 10 mmag precision. Most of these objects are highly reddened and deep in the Galactic disk, probing the structure and properties of the Milky Way and its interstellar medium. The full survey is publicly available.
Motivated by the observed differences in the nebular emission of nearby and high-redshift galaxies, we carry out a set of direct numerical simulations of turbulent astrophysical media exposed to a UV background. The simulations assume a metallicity of $Z/Z_{\odot}$=0.5 and explicitly track ionization, recombination, charge transfer, and ion-by-ion radiative cooling for several astrophysically important elements. Each model is run to a global steady state that depends on the ionization parameter $U$, and the one-dimensional turbulent velocity dispersion, $\sigma_{\rm 1D}$, and the turbulent driving scale. We carry out a suite of models with a T=42,000K blackbody spectrum, $n_e$ = 100 cm$^{-3}$ and $\sigma_{\rm 1D}$ ranging between 0.7 to 42 km s$^{-1},$ corresponding to turbulent Mach numbers varying between 0.05 and 2.6. We report our results as several nebular diagnostic diagrams and compare them to observations of star-forming galaxies at a redshift of $z\approx$2.5, whose higher surface densities may also lead to more turbulent interstellar media. We find that subsonic, transsonic turbulence, and turbulence driven on scales of 1 parsec or greater, have little or no effect on the line ratios. Supersonic, small-scale turbulence, on the other hand, generally increases the computed line emission. In fact with a driving scale $\approx 0.1$ pc, a moderate amount of turbulence, $\sigma_{\rm 1D}$=21-28 km s$^{-1},$ can reproduce many of the differences between high and low redshift observations without resorting to harder spectral shapes.
We present photometric redshifts for 1,031 X-ray sources in the X-ATLAS field, using the machine learning technique TPZ (Carrasco Kind & Brunner 2013). X-ATLAS covers 7.1 deg2 observed with the XMM-Newton within the Science Demonstration Phase (SDP) of the H-ATLAS field, making it one of the largest contiguous areas of the sky with both XMMNewton and Herschel coverage. All of the sources have available SDSS photometry while 810 have additionally mid-IR and/or near-IR photometry. A spectroscopic sample of 5,157 sources primarily in the XMM/XXL field, but also from several X-ray surveys and the SDSS DR13 redshift catalogue, is used for the training of the algorithm. Our analysis reveals that the algorithm performs best when the sources are split, based on their optical morphology, into point-like and extended sources. Optical photometry alone is not enough for the estimation of accurate photometric redshifts, but the results greatly improve when, at least, mid-IR photometry is added in the training process. In particular, our measurements show that the estimated photometric redshifts for the X-ray sources of the training sample, have a normalized absolute median deviation, n_mad=0.06, and the percentage of outliers, eta=10-14 percent, depending on whether the sources are extended or point-like. Our final catalogue contains photometric redshifts for 933 out of the 1,031 X-ray sources with a median redshift of 0.9.
The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models. The Herschel surveys reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a a single Galaxy Sequence (GS) rather than a star-forming `main sequence' and a separate region of `passive' or `red-and-dead' galaxies. The form of the GS is now clearer because far-infrared surveys such as the Herschel ATLAS pick up a population of optically-red star-forming galaxies that would have been classified as passive using most optical criteria. The space-density of this population is at least as high as the traditional star-forming population. By stacking spectra of H-ATLAS galaxies over the redshift range 0.001 < z < 0.4, we show that the galaxies responsible for the rapid low-redshift evolution have high stellar masses, high star-formation rates but, even several billion years in the past, old stellar populations - they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today. The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution. We propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population.
In this study, we present a suite of high-resolution numerical simulations of an isolated galaxy to test a sub-grid framework to consistently follow the formation and dissociation of H$_2$ with non-equilibrium chemistry. The latter is solved via the package KROME, coupled to the mesh-less hydrodynamic code GIZMO. We include the effect of star formation (SF), modelled with a physically motivated prescription independent of H$_2$, supernova feedback and mass losses from low-mass stars, extragalactic and local stellar radiation, and dust and H$_2$ shielding, to investigate the emergence of the observed correlation between H$_2$ and SF rate surface densities. We present two different sub-grid models and compare them with on-the-fly radiative transfer (RT) calculations, to assess the main differences and limits of the different approaches. We also discuss a sub-grid clumping factor model to enhance the H$_2$ formation, consistent with our SF prescription, which is crucial, at the achieved resolution, to reproduce the correlation with H$_2$. We find that both sub-grid models perform very well relative to the RT simulation, giving comparable results, with moderate differences, but at much lower computational cost. We also find that, while the Kennicutt-Schmidt relation for the total gas is not strongly affected by the different ingredients included in the simulations, the H$_2$-based counterpart is much more sensitive, because of the crucial role played by the dissociating radiative flux and the gas shielding.
We analyze age-velocity dispersion relations (AVRs) from kinematics of individual stars in eight Local Group galaxies ranging in mass from Carina ($M_{*} \sim 10^{6}$) to M31 ($M_{*} \sim 10^{11}$). Observationally the $\sigma$ vs. stellar age trends can be interpreted as dynamical heating of the stars by GMCs, bars/spiral arms, or merging subhalos; alternatively the stars could have simply been born out of a more turbulent ISM at high redshift and retain that larger velocity dispersion till present day - consistent with recent IFU studies. To ascertain the dominant mechanism and better understand the impact of instabilities and feedback, we develop models based on observed SFHs of these Local Group galaxies in order to create an evolutionary formalism which describes the ISM velocity dispersion due to a galaxy's evolving gas fraction. These empirical models relax the common assumption that the stars are born from gas which has constant velocity dispersion at all redshifts. Using only the observed SFHs as input, the ISM velocity dispersion and a mid-plane scattering model fits the observed AVRs of low mass galaxies without fine tuning. Higher mass galaxies above $M_{vir} > 10^{11}$ need a larger contribution from latent dynamical heating processes (for example minor mergers), in excess of the ISM model. Using the SFHs we also find that supernovae feedback does not appear to be a dominant driver of the gas velocity dispersion compared to gravitational instabilities - at least for dispersions $\sigma \gtrsim 25$ km/s. Together our results point to stars being born with a velocity dispersion close to that of the gas at the time of their formation, with latent dynamical heating operating with a galaxy mass-dependent efficiency. These semi-empirical relations may help constrain the efficiency of feedback and its impact on the physics of disk settling in galaxy formation simulations.
We investigate the stellar mass loss of gas rich galaxies falling into clusters due to the change in the gravitational potential caused by the ram pressure stripping of their gas. We model the satellites with exponential stellar and gas disk profiles, assume rapid ram pressure stripping, and follow the stellar orbits in the shocked potential. Due to the change of the potential, the stars move from circular orbits to elliptical orbits with apocenters that are often outside the tidal radius, causing those stars to be stripped. We explore the impact of the redshift of infall, gas fraction, satellite halo mass and cluster mass on this process. The puffing of the satellites makes them appear as ultra diffuse galaxies, and the stripped stars contribute to the intracluster light. Our results show these effects are most significant for less-massive satellites, which have larger gas fractions when they are accreted into clusters. The preferential destruction of low mass systems causes the red fraction of cluster galaxies to be smaller at lower masses, an observation that is otherwise difficult to explain.
In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in-situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this work we focus on the outer regions of the Milky Way stellar halo, by determining chemical abundances of halo stars with large present-day Galactocentric distances, $>$15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, $-3.1 \lesssim$[Fe/H]$\lesssim -0.6$. We show that the ratio of $\alpha$-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H]$\gtrsim -1.5$ when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples.
We present magnitudes and profile fits for 180 galaxies in the central field of the massive lensing cluster Abell 1689 using very deep imaging with the ACS/HST in the F814W bandpass. Previous work revealed an exceptionally large number of globular clusters (GCs) in A1689 and mapped their number density distribution. We decompose this number density map into GCs associated with individual cluster galaxies and ICGCs (intracluster globular clusters) associated with the intracluster light (ICL). In all, we measure GC specific frequencies $S_N$ for 33 cluster members and the ICL. The relation between $S_N$ and galaxy magnitude is consistent with the trend observed in Virgo, although some intermediate luminosity galaxies scatter to $S_N>10$. We estimate the ICL makes up 11% of the starlight in this field, whereas the ICGCs account for $\sim\,$35% of the GCs, both consistent with predictions from simulations. Galaxies with higher $S_N$ values tend to be rounder, and there is a marginally significant trend of decreasing $S_N$ with increasing specific angular momenta $\lambda_R$. We also reevaluate the GC population in the A2744 Frontier Field, for which fewer than one-tenth as many GCs have been detected because of its larger distance. Finally, our core-S\'ersic fit to the light profile of the A1689 BCG implies a break radius of 3.8kpc, among the largest known; we discuss implications of the sizable core and extensive GC population for the supermassive black hole in light of scaling relations.
The globular cluster systems of galaxies are well-known to extend to large galactocentric radii. Here we quantify the size of GC systems using the half number radius of 22 GC systems around early-type galaxies from the literature. We compare GC system sizes to the sizes and masses of their host galaxies. We find that GC systems typically extend to 4$\times$ that of the host galaxy size, however this factor varies with galaxy stellar mass from about 3$\times$ for M$^{\ast}$ galaxies to 5$\times$ for the most massive galaxies in the universe. The size of a GC system scales approximately linearly with the virial radius (R$_{200}$) and with the halo mass (M$_{200}$) to the 1/3 power. The GC system of the Milky Way follows the same relations as for early-type galaxies. For Ultra Diffuse Galaxies their GC system size scales with halo mass and virial radius as for more massive, larger galaxies. UDGs indicate that the linear scaling of GC system size with stellar mass for massive galaxies flattens out for low stellar mass galaxies. Our scalings are different to those reported recently by Hudson \& Robison (2017).
We introduce a new theoretical model to describe the emitting region in a blazar jet. We assume a one-zone leptonic picture, and construct the particle transport equation for a plasma blob experiencing low-energy, monoenergetic particle injection, energy dependent particle escape, shock acceleration, adiabatic expansion, stochastic acceleration, synchrotron radiation, and external Compton radiation from the dust torus and broad line region. We demonstrate that a one-zone leptonic model is able to explain the IR though {\gamma}-ray spectrum for 3C 279 in 2008-2009. We determine that the broad-line region seed photons cannot be adequately described by a single average distribution, but rather we find that a stratified broad line region provides an improvement in the estimation of the distance of the emitting region from the black hole. We calculate that the jet is not always in equipartition between the particles and magnetic field, and find that stochastic acceleration provides more energy to the particles than does shock acceleration, where the latter is also overshadowed by adiabatic losses. We further introduce a novel technique to implement numerical boundary conditions and determine the global normalization for the electron distribution, based on analysis of stiff ordinary differential equations. Our astrophysical results are compared with those obtained by previous authors.
I studied giant discy galaxies with optical radii more than 30 kpc. The comparison of these systems with discy galaxies of moderate sizes revealed that they tend to have higher rotation velocities, B-band luminosities, HI masses and dark-to-luminous mass ratios. The giant discs follow the trend $\log(M_{\rm HI})(R_{25})$ found for normal size galaxies. It indicates the absence of the peculiarities of evolution of star formation in these galaxies. The HI mass to luminosity ratio of giant galaxies appears not to differ from that of normal size galaxies, giving evidences in favor of similar star formation efficiency. I also found that the bars and rings occur more frequently among giant discs. I performed mass-modelling of the subsample of 18 giant galaxies with available rotation curves and surface photometry data and constructed $\chi^2$ maps for the parameters of their dark matter haloes. These estimates indicate that giant discs tend to be formed in larger more massive and rarified dark haloes in comparison to moderate size galaxies. However giant galaxies do not deviate significantly from the relations between the optical sizes and dark halo parameters for moderate size galaxies. These findings can rule out the catastrophic scenario of the formation of at least most of giant discs, since they follow the same relations as normal discy galaxies. The giant sizes of the discs can be due to the high radial scale of the dark matter haloes in which they were formed.
We present a kinematic study of the nuclear stellar disk in M31 at infrared wavelengths using high spatial resolution integral field spectroscopy. The spatial resolution achieved, FWHM = 0."12 (0.45 pc at the distance of M31), has only previously been equaled in spectroscopic studies by space-based long-slit observations. Using adaptive optics-corrected integral field spectroscopy from the OSIRIS instrument at the W. M. Keck Observatory, we map the line-of-sight kinematics over the entire old stellar eccentric disk orbiting the supermassive black hole (SMBH) at a distance of r<4 pc. The peak velocity dispersion is 381+/-55 km/s , offset by 0.13 +/- 0.03 from the SMBH, consistent with previous high-resolution long-slit observations. There is a lack of near-infrared (NIR) emission at the position of the SMBH and young nuclear cluster, suggesting a spatial separation between the young and old stellar populations within the nucleus. We compare the observed kinematics with dynamical models from Peiris & Tremaine (2003). The best-fit disk orientation to the NIR flux is [$\theta_l$, $\theta_i$, $\theta_a$] = [-33 +/- 4$^{\circ}$, 44 +/- 2$^{\circ}$, -15 +/- 15$^{\circ}$], which is tilted with respect to both the larger-scale galactic disk and the best-fit orientation derived from optical observations. The precession rate of the old disk is $\Omega_P$ = 0.0 +/- 3.9 km/s/pc, lower than the majority of previous observations. This slow precession rate suggests that stellar winds from the disk will collide and shock, driving rapid gas inflows and fueling an episodic central starburst as suggested in Chang et al. (2007).
We present HI synthesis imaging of the giant elliptical galaxy IC 1459 and its surroundings with the Australia Telescope Compact Array (ATCA). Our search for extended HI emission revealed a large complex of HI clouds near IC 1459, likely the debris from tidal interactions with neighbouring galaxies. The total HI mass ($\sim 10^9$\Msun) in the detected clouds spans 250 kpc from the north-east of the gas-rich spiral NGC 7418A to the south-east of IC 1459. The extent and mass of the HI debris, which shows rather irregular morphology and kinematics, are similar to those in other nearby groups. Together with HI clouds recently detected near two other IC 1459 group members, namely IC 5270 and NGC 7418, using Phased-Array Feeds (PAFs) on the Australian Square Kilometer Array Pathfinder (ASKAP), the detected debris make up a significant fraction of the group's intergalactic medium.
We present an 8 pc x 5 pc resolution view of the central ~ 200 pc region of the nearby starburst galaxy NGC 253, based on ALMA Band 7 ({\lambda} ~ 0.85 mm or {\nu} ~ 350 GHz) observations covering 11 GHz. We resolve the nuclear starburst of NGC 253 into eight dusty star-forming clumps, 10 pc in scale, for the first time. These clumps, each of which contains (4-10) x 10^4 M_sun of dust (assuming that the dust temperature is 25 K) and up to 6 x 10^2 massive (O5V) stars, appear to be aligned in two parallel ridges, while they have been blended in previous studies. Despite the similarities in sizes and dust masses of these clumps, their line spectra vary drastically from clump to clump although they are separated by only ~ 10 pc. Specifically, one of the clumps, Clump 1, exhibits line confusion-limited spectra with at least 36 emission lines from 19 molecules (including CH3OH, HNCO, H2CO, CH3CCH, H2CS, and H3O+) and a hydrogen recombination line (H26{\alpha}), while much fewer kinds of molecular lines are detected in some other clumps where fragile species, such as complex organic molecules and HNCO, completely disappear from their spectra. We demonstrate the existence of hot molecular gas ($T_rot (SO2) = 90 {\pm} 11 K) in the former clump, which suggests that the hot and chemically rich environments are localized within a 10-pc scale star-forming clump.
One of the major unsolved questions on the understanding of the AGN population is the origin of the dichotomy between radio-quiet and radio-loud quasars. The most promising explanation is provided by the spin paradigm, which suggests radio-loud quasars have higher black hole spin. However, the measurement of black hole spin remains extremely challenging. We here aim at comparing the mean radiative efficiencies of carefully matched samples of radio-loud and radio-quiet SDSS quasars at 0.3<z<0.8. We use the [OIII] luminosity as an indirect average tracer of the ionizing continuum in the extreme-UV regime where differences in the SED due to black hole spin are most pronounced. We find that the radio-loud sample shows an enhancement in [OIII] line strength by a factor of at least 1.5 compared to a radio-quiet sample matched in redshift, black hole mass and optical continuum luminosity or accretion rate. We argue that this enhancement is caused by differences in the SED, suggesting higher average bolometric luminosities at fixed accretion rate in the radio-loud population. This suggests that the radio-loud quasar population has on average systematically larger radiative efficiencies and therefore higher black hole spin than the radio-quiet population, providing observational support for the black hole spin paradigm.
Cross-identifying complex radio sources with optical or infra red (IR) counterparts in surveys such as the Australia Telescope Large Area Survey (ATLAS) has traditionally been performed manually. However, with new surveys from the Australian Square Kilometre Array Pathfinder (ASKAP) detecting many tens of million of radio sources such an approach is no longer feasible. This paper presents new software (LRPY - Likelihood Ratio in PYthon) to automate the process of cross-identifying radio sources with catalogues at other wavelengths. LRPY implements the Likelihood Ratio (LR) technique with a modification to account for two galaxies contributing to a sole measured radio component. We demonstrate LRPY by applying it to ATLAS DR3 and a {\it Spitzer}-based multi-wavelength fusion catalogue, identifying 3,848 matched sources via our LR-based selection criteria. A subset of 1987 sources have flux density values for all IRAC bands which allow us to use criteria to distinguish between active galactic nuclei (AGN) and star-forming galaxies (SFG). We find that 936 radio sources ($\approx47\,\%$) meet both of the Lacy and Stern AGN selection criteria. Of the matched sources, 295 have spectroscopic redshifts and we examine the radio to IR flux ratio vs redshift, proposing an AGN selection criterion below the Elvis radio-loud (RL) AGN limit for this dataset. Taking the union of all three AGN selection criteria we identify 956 as AGN ($\approx48\,\%$). From this dataset, we find a decreasing fraction of AGN with lower radio flux densities consistent with other results in the literature.
As part of the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) project we present an estimate of the mass of the supermassive black hole (SMBH) in the nearby fast-rotating early-type galaxy NGC4429, that is barred and has a boxy/peanut-shaped bulge. This estimate is based on Atacama Large Millimeter/submillimeter Array (ALMA) cycle-2 observations of the 12CO(3-2) emission line with a linear resolution of ~13 pc (0"18x0"14). NGC4429 has a relaxed, flocculent nuclear disc of molecular gas that is truncated at small radii, likely due to the combined effects of gas stability and tidal shear. The warm/dense 12CO(3-2) emitting gas is confined to the inner parts of this disc, likely again because the gas becomes more stable at larger radii, preventing star formation. The gas disc has a low velocity dispersion of 2.2$^{+0.68}_{-0.65}$ km/s. Despite the inner truncation of the gas disc, we are able to model the kinematics of the gas and estimate a mass of (1.5$\pm0.1^{+0.15}_{-0.35}$)$\times$10$^8$ Msun for the SMBH in NGC4429 (where the quoted uncertainties reflect the random and systematic uncertainties, respectively), consistent with a previous upper limit set using ionised gas kinematics. We confirm that the V-band mass-to-light ratio changes by ~30% within the inner 400 pc of NGC4429, as suggested by other authors. This SMBH mass measurement based on molecular gas kinematics, the sixth presented in the literature, once again demonstrates the power of ALMA to constrain SMBH masses.
The Milky Way is a barred galaxy whose central bulge has a box/peanut shape and consists of multiple stellar populations with different orbit distributions. This review describes dynamical and chemo-dynamical equilibrium models for the Bulge, Bar, and inner Disk based on recent survey data. Some of the highlighted results include (i) stellar mass determinations for the different Galactic components, (ii) the need for a core in the dark matter distribution, (iii) a revised pattern speed putting corotation at ~6 kpc, (iv) the strongly barred distribution of the metal-rich stars, and (v) the radially varying dynamics of the metal-poor stars which is that of a thick disk-bar outside ~1 kpc, but changes into an inner centrally concentrated component with several possible origins. On-going and future surveys will refine this picture, making the Milky Way a unique case for studying how similar galaxies form and evolve.
We discuss the origin of the LMC stellar bar by comparing the star formation histories (SFH) obtained from deep color-magnitude diagrams (CMDs) in the bar and in a number of fields in different directions within the inner disk. The CMDs, reaching the oldest main sequence turnoffs in these very crowded fields, have been obtained with VIMOS on the VLT in service mode, under very good seeing conditions. We show that the SFHs of all fields share the same patterns, with consistent variations of the star formation rate as a function of time in all of them. We therefore conclude that no specific event of star formation can be identified with the formation of the LMC bar, which instead likely formed from a redistribution of disk material that occurred when the LMC disk became bar unstable, and shared a common SFH with the inner disk thereafter. The strong similarity between the SFH of the center and edge of the bar rules out significant spatial variations of the SFH across the bar, which are predicted by scenarios of classic bar formation through buckling mechanisms.
We present a detailed study of the molecular gas in the fast AGN-driven outflow in the nearby radio-loud Seyfert galaxy IC 5063. Using ALMA observations of a number of tracers (12CO(1-0), 12CO(2-1), 12CO(3-2), 13CO(2-1) and HCO+(4-3)), we map the differences in excitation, density and temperature of the gas. The results show that in the immediate vicinity of the radio jet, a fast outflow, with velocities up to 800 km/s, is occurring of which the gas has high excitation temperatures in the range 30-55 K, demonstrating the direct impact of the jet on the ISM. The relative brightness of the CO lines show that the outflow is optically thin. We estimate the mass of the molecular outflow to be 1.2 x 10^6 Msol and likely to be a factor 2-3 larger. This is similar to that of the outflow of atomic gas, but much larger than that of the ionised outflow, showing that the outflow is dominated by cold gas. The total mass outflow rate we estimate to be ~12 Msol/yr. The mass of the outflow is much smaller than the total gas mass of the ISM of IC 5063. Therefore, although the influence of the radio jet is very significant in the inner regions, globally speaking the impact will be very modest. We use RADEX modelling to explore the physical conditions of the molecular gas in the outflow. Models with the outflowing gas being quite clumpy give the most consistent results and our preferred solutions have kinetic temperatures in the range 20-100 K and densities between 10^5 and 10^6 cm^-3. The resulting pressures are 10^6-10^7.5 K cm^-3, about two orders of magnitude higher than in the outer quiescent disk. The results strongly suggest that the outflow is driven by the radio jet expanding into a clumpy medium, creating a cocoon of gas which is pushed away from the jet axis resulting in a lateral outflow, very similar to what is predicted by numerical simulations.
We present the second Multi-Epoch X-ray Serendipitous AGN Sample (MEXSAS2), extracted from the 6th release of the XMM Serendipitous Source Catalogue (XMMSSC-DR6), cross-matched with Sloan Digital Sky Survey quasar catalogues DR7Q and DR12Q. Our sample also includes the available measurements for masses, bolometric luminosities, and Eddington ratios. Analyses of the ensemble structure function and spectral variability are presented, together with their dependences on such parameters. We confirm a decrease of the structure function with the X-ray luminosity, and find a weak dependence on the black hole mass. We introduce a new spectral variability estimator, taking errors on both fluxes and spectral indices into account. We confirm an ensemble softer when brighter trend, with no dependence of such estimator on black hole mass, Eddington ratio, redshift, X-ray and bolometric luminosity.
We built a 8um selected sample of galaxies in the NEP-AKARI field by defining 4 redshift bins with the four AKARI bands at 11, 15, 18 and 24 microns (0.15<z<0.49, 0.75<z<1.34, 1.34<z<1.7 and 1.7<z<2.05) . Our sample contains 4079 sources, 599 are securely detected with Herschel/PACS. Also adding ultraviolet (UV) data from GALEX, we fit the spectral energy distributions using the physically motivated code CIGALE to extract the star formation rate, stellar mass, dust attenuation and the AGN contribution to the total infrared luminosity (L_{IR}). We discuss the impact of the adopted attenuation curve and that of the wavelength coverage to estimate these physical parameters. We focus on galaxies with a luminosity close the characteristic L_{IR}^* in the different redshift bins to study the evolution with redshift of the dust attenuation in these galaxies.
The NGC 5903 galaxy group is a nearby (~30 Mpc) system of ~30 members, dominated by the giant ellipticals NGC 5903 and NGC 5898. The group contains two unusual structures, a ~110 kpc long HI filament crossing NGC 5903, and a ~75 kpc wide diffuse, steep-spectrum radio source of unknown origin which overlaps NGC 5903 and appears to be partly enclosed by the HI filament. Using a combination of Chandra, XMM-Newton, GMRT and VLA observations, we detect a previously unknown ~0.65 keV intra-group medium filling the volume within 145 kpc of NGC 5903, and find a loop of enhanced X-ray emission extending ~35 kpc southwest from the galaxy, enclosing the brightest part of the radio source. The northern and eastern parts of this X-ray structure are also strongly correlated with the southern parts of the HI filament. We determine the spectral index of the bright radio emission to be $\alpha_{150}^{612}$=1.03$\pm$0.08, indicating a radiative age >360 Myr. We discuss the origin of the correlated radio, X-ray and HI structures, either through an interaction-triggered AGN outburst with enthalpy 1.8x10$^{57}$ erg, or via a high-velocity collision between a galaxy and the HI filament. While neither scenario provides a complete explanation, we find that an AGN outburst is the most likely source of the principal X-ray and radio structures. However, it is clear that galaxy interactions continue to play an important role in the development of this relatively highly evolved galaxy group. We also resolve the question of whether the group member galaxy ESO 514-3 hosts a double-lobed radio source, confirming that the source is a superposed background AGN.
In an earlier paper we presented Jansky Very Large Array multi-frequency, multi-array continuum imaging of a unique sample of low axial-ratio radio galaxies. In this paper, the second in the series, we examine the images to know the phenomenology of how the off-axis emission relates to the main radio source. Inversion symmetric offset emission appears to be bimodal and to originate from one of two strategic locations: outer ends of radio lobes (Outer-deviation) or from inner ends (Inner-deviation). The latter sources are almost always associated with edge-brightened sources. With S- and Z-shaped sources being a subset of Outer-deviation sources this class lends itself naturally to explanations involving black hole axis precession. Our data allow us to present a plausible model for the more enigmatic Inner-deviation sources with impressive wings; as for outer-deviation sources these too require black hole axis shifts although also requiring plasma backflows into relic channels. Evolution in morphology over time relates the variety in structures in inner-deviation sources including XRGs. With features such as non-collinearities, central inner-S "spine", corresponding lobe emission peaks, double and protruding hotspots not uncommon, black hole axis precession, drifts, or flips could be active in significant fraction of radio sources with prominent off-axis emission. At least 4\% of radio galaxies appear to undergo black hole axis rotation. Quasars offer a key signature to recognize rotating axes. With rich haul of sources that have likely undergone axis rotation our work shows the usefulness of low axial-ratio sources to pursue searches for binary supermassive black holes.
Galaxy clusters are the largest virialized structures in the observable
Universe. The knowledge of their properties provides many useful astrophysical
and cosmological information.
Our aim is to derive the luminosity and stellar mass profiles of the nearby
galaxy clusters of the Omega-WINGS survey and to study the main scaling
relations valid for such systems.
We have merged the data of the WINGS and Omega-WINGS databases, sorted the
sources according to the distance from the brightest cluster galaxy (BCG) and
calculated the integrated luminosity profiles in the $B$ and $V$ bands, taking
into account extinction, photometric and spatial completeness, K-correction and
background contribution. Then, by exploiting the spectroscopic sample we
derived the stellar mass profiles of the clusters.
We got the luminosity profiles of 46 galaxy clusters, reaching $r_{200}$ in
30 cases, and the stellar mass profiles of 42 of our objects. We successfully
fitted all the integrated luminosity growth profiles with one or two embedded
S\'ersic components, deriving the main clusters parameters.
Finally, we checked the main scaling relation among the clusters parameters
in comparison with those obtained for a selected sample of early-type galaxies
(ETGs) of the same clusters.
We found that the nearby galaxy clusters are non-homologous structures like
ETGs and exhibit a color-magnitude (CM) red-sequence relation very similar to
that observed for galaxies in clusters. These properties are not expected in
the current cluster formation scenarios. In particular the existence of a CM
relation for clusters, shown here for the first time, suggests that the
baryonic structures grow and evolve in a similar way at all scales.
Near-infrared (IR) diffuse Galactic light (DGL) consists of scattered light and thermal emission from interstellar dust grains illuminated by interstellar radiation field (ISRF). At 1.25 and 2.2um, recent observational study shows that intensity ratios of the DGL to interstellar 100um dust emission steeply decrease toward high Galactic latitudes (b). In this paper, we investigate origin(s) of the b-dependence on the basis of models of thermal emission and scattered light. Combining a thermal emission model with regional variation of the polycyclic aromatic hydrocarbon abundance observed with Planck, we show that contribution of the near-IR thermal emission component to the observed DGL is less than ~20%. We also examine the b-dependence of the scattered light, assuming a plane-parallel Galaxy with smooth distributions of the ISRF and dust density along vertical direction, and assuming a scattering phase function according to a recently developed model of interstellar dust. We normalize the scattered light intensity to the 100um intensity corrected for deviation from the cosecant-b law according to the Planck observation. As the result, the present model taking all the b-dependence of dust and ISRF properties can account for the observed b-dependence of the near-IR DGL. However, uncertainty of the correction for the 100um emission is large and other normalizing quantities may be appropriate for more robust analysis of the DGL.
We wish to put tight constraints on the possible contribution of an MHD disk wind (DW) to the HH212 molecular jet. We use ALMA Cycle 4 to map the inner outflow at $0.13" \sim$ 60~au resolution, and compare with synthetic predictions for DW models. We identify in SO/SO$_2$ a rotating flow wider and slower than the axial SiO jet. The broad outflow cavity seen in C$^{34}$S is not carved by a fast wide-angle wind but by this slower agent. Rotation signatures may be fitted by a DW of moderate lever arm launched out to $\sim$ 40 au, with SiO tracing dust-free streamlines from 0.05-0.3 au. If indeed a DW, it could limit the core-to-star efficiency to $\leq 50\%$.
Upcoming cosmic microwave background (CMB) surveys will soon make the first detection of the polarized Sunyaev-Zel'dovich effect, the linear polarization generated by the scattering of CMB photons on the free electrons present in collapsed objects. Measurement of this polarization along with knowledge of the electron density of the objects allows a determination of the quadrupolar temperature anisotropy of the CMB as viewed from the space-time location of the objects. Maps of these remote temperature quadrupoles have several cosmological applications. Here we propose a new application: reconstruction of the cosmological reionization history. We show that with quadrupole measurements out to redshift 3, constraints on the mean optical depth can be improved by an order of magnitude beyond the CMB cosmic variance limit.
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We have conducted a search of a 9 deg$^{2}$ region of the CFHTLS around the Milky Way analog M101 (D$\sim$7 Mpc), in order to look for previously unknown low surface brightness galaxies. This search has uncovered 38 new low surface brightness dwarf candidates, and confirmed 11 previously reported galaxies, all with central surface brightness $\mu$(g,0)$>$23mag/arcsec$^{2}$, potentially extending the satellite luminosity function for the M101 group by $\sim$1.2 magnitudes. The search was conducted using an algorithm that nearly automates the detection of diffuse dwarf galaxies. The candidates small size and low surface brightness means that the faintest of these objects would likely be missed by traditional visual or computer detection techniques. The dwarf galaxy candidates span a range of $-$7.1 $\geq$ M$_g$ $\geq$ $-$10.2 and half light radii of 118-540 pc at the distance of M101, and they are well fit by simple S\'{e}rsic surface brightness profiles. These properties are consistent with dwarfs in the Local Group, and to match the Local Group luminosity function $\sim$10-20 of these candidates should be satellites of M101. Association with a massive host is supported by the lack of detected star formation and the over density of candidates around M101 compared to the field. The spatial distribution of the dwarf candidates is highly asymmetric, and concentrated to the northeast of M101 and therefore distance measurements will be required to determine if these are genuine members of the M101 group.
The young cluster NGC 6231 (stellar ages ~2-7 Myr) is observed shortly after star-formation activity has ceased. Using the catalog of 2148 probable cluster members obtained from Chandra, VVV, and optical surveys (Paper I), we examine the cluster's spatial structure and dynamical state. The spatial distribution of stars is remarkably well fit by an isothermal sphere with moderate elongation, while other commonly used models like Plummer spheres, multivariate normal distributions, or power-law models are poor fits. The cluster has a core radius of $1.2\pm0.1$ pc and a central density of ~200 stars pc$^{-3}$. The distribution of stars is mildly mass segregated. However, there is no radial stratification of the stars by age. Although most of the stars belong to a single cluster, a small subcluster of stars is found superimposed on the main cluster, and there are clumpy non-isotropic distributions of stars outside ~4 core radii. When the size, mass, and age of NGC 6231 are compared to other young star clusters and subclusters in nearby active star-forming regions, it lies at the high-mass end of the distribution but along the same trend line. This could result from similar formation processes, possibly hierarchical cluster assembly. We argue that NGC 6231 has expanded from its initial size but that it remains gravitationally bound.
We describe the hCOSMOS redshift survey of the COSMOS field conducted with the Hectospec spectrograph on the MMT. In the central 1 deg$^2$, the hCOS20.6 subset of the survey is $>90\%$ complete to a limiting $r=20.6$. The hCOSMOS survey includes 1701 new redshifts in the COSMOS field. We also use the total of 4362 new and remeasured objects to derive the age sensitive D$_n4000$ index over the entire redshift interval $0.001\lesssim z\lesssim0.6$. For $85\%$ of the quiescent galaxies in the hCOS20.6, we measure the central line-of-sight velocity dispersion. To explore potential uses of this survey, we combine previously measured galaxy sizes, profiles and stellar masses with the spectroscopy. The comparison reveals the known relations among structural, kinematic, and stellar population properties. We also compare redshift and D$_n4000$ distributions of hCOS20.6 galaxies with SHELS; a complete spectroscopic survey of 4 deg$^2$ observed to the same depth. The redshift distributions in the two fields are very different but the D$_n4000$ distribution is remarkably similar. Using measured velocity dispersions, we test a photometric proxy calibrated to galaxies in the local universe. The systematic differences between the measured and predicted velocity dispersions are correlated with galaxy dynamical and stellar population properties reinforcing the importance of direct spectroscopic measurements.
The fraction of Lyman-$\alpha$ emitters among the galaxy population has been found to increase from $z\sim0$ to $z\sim6$ and drop dramatically at $z>6$. This drop has been interpreted as an effect of an increasingly neutral intergalactic medium with increasing redshift, while a LyC escape fraction evolving with redshift. We report the result of a large VLT/FORS2 program aiming to confirm spectroscopically a large galaxy sample at $z\geq6$ that has been selected in several independent fields through the Lyman Break technique. Combining those data with archival data, we create a large and homogeneous sample of $z\sim6$ galaxies ($N=127$), complete in terms of Ly$\alpha$ detection at $>95\%$ for EW(Ly$\alpha)\geq25\AA$. We use this sample to derive a new measurement of the LAE fraction at $z\sim6$ and derive the physical properties of these galaxies through spectral energy distribution fitting. We find a median LAE fraction at $z\sim6$ lower than in previous studies. The main difference between LAEs and non-LAEs is that the latter are significantly dustier. Using predictions of our SED fitting code accounting for nebular emission, we find an effective Ly$\alpha$ escape fraction $f^{eff}_{esc}(Ly\alpha)=0.23^{+0.36}_{-0.17}$ remarkably consistent with the value derived by comparing UV luminosity function with Ly$\alpha$ luminosity function. We conclude that the drop in the LAE fraction from $z\sim6$ to $z>6$ is less dramatic than previously found and the effect of an increasing IGM neutral fraction is possibly observed at $5<z<6$. Based on our derived $f^{eff}_{esc}(Ly\alpha)$, we find that the IGM has a relatively small impact on Ly$\alpha$ photon visibility at $z\sim6$, with a lower limit for the IGM transmission to \lya\ photons, $T_{IGM}\gtrsim0.20$, likely due to the presence of outflows. [abdridged]
ALMA imaging of the cold molecular medium in the nearby starburst galaxy NGC 1808 is presented. The observations reveal the distribution of molecular gas, traced by $^{12}$CO (1-0) and $^{12}$CO (3-2), and continuum (93 and 350 GHz) across the central 1 kpc starburst region at high resolution of $\sim1$ arcsec. A molecular gas torus (radius $\sim30$ pc) is discovered in the circumnuclear disk (CND; central 100 pc), with a high CO (3-2)/CO (1-0) ratio of $\sim1$, surrounded by massive ($10^6$-$10^7$ $M_\odot$) clouds with high star formation efficiency (SFE$\sim10^{-8}$ yr$^{-1}$), molecular spiral arms, and a 500 pc pseudoring. The CND harbors a continuum core and molecular gas exhibiting peculiar motion. The new data confirm the line splitting along the minor galactic axis, interpreted as a nuclear gas outflow with average velocity $\sim180$ km s$^{-1}$, and show evidence of a velocity gradient of $\sim+0.4$ km s$^{-1}$ pc$^{-1}$ along the axis. In addition, supershells expanding from the 500 pc ring with maximum velocities of $\sim75$ km s$^{-1}$ are revealed. The distribution and CO luminosities of molecular clouds in the central 1 kpc starburst region indicate an evolutionary sequence, from gas accretion onto the 500 pc ring from the large-scale bar, to enhanced star formation in the ring, and outflow as feedback.
We study the effect of anisotropic radiation illumination on the alignment of polycyclic aromatic hydrocarbons (PAHs) and report that cross section mechanism of alignment earlier considered in terms of gas-grain interactions can also be efficient for the photon-grain interaction. We demonstrate this by first calculate the angle-dependence rotational damping and excitation coefficients by photon absorption followed by infrared emission and average the coefficients over internal thermal fluctuations. Then, we calculate the degree of PAH alignment for the different environments and physical parameters, including the illumination direction, ionization fraction, and magnetic field strength. For the reflection nebula (RN) conditions with unidirectional radiation field, we find that the degree of alignment tends to increase with increasing the angle $\psi$ between the illumination direction and the magnetic field, as a result of the decrease of the cross-section of photon absorption with $\psi$. We calculate the polarization of spinning PAH emission using the obtained degree of alignment for the different physical parameters. We find that the polarization of spinning PAH emission from RN can be large, between $5-20\%$ for frequency $\nu > 20$GHz, whereas the polarization is less than $3\%$ for photodissociation regions (PDRs) with much higher gas density. The polarization for the diffuse cold neutral medium (CNM) is rather low, below $1\%$ for $\nu>20$GHz, consistent with observations by WMAP and Planck. Our results demonstrate that the RNe are the favored environment to observe the polarization of spinning dust emission as well as polarized mid-IR emission from PAHs.
The Canis Major OB1 Association has an intriguing scenario of star formation, especially in the Canis Major R1 (CMa R1) region traditionally assigned to a reflection nebula, but in reality an ionized region. This work is focused on the young stellar population associated to CMa R1, for which our previous results from ROSAT, optical and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star-formation episodes. The X-ray data allow the detected sources to be characterized according to hardness ratios, light curves and spectra. Estimates of mass and age were obtained from the 2MASS catalogue, and used to define a complete subsample of stellar counterparts, for statistical purposes. A catalogue of 387 XMM-Newton sources is provided, 78% being confirmed as members or probable members of the CMa R1 association. Flares were observed for 13 sources, and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. We found a minimum value of log(L$_{X}$[erg/s]) = 29.43, indicating that our sample of low-mass stars ($M_\star \leq 0.5 M_\odot$), being faint X-ray emitters, is incomplete. Among the 250 objects selected as our complete subsample (defining our "best sample"), 171 are found to the East of the cloud, near Z CMa and dense molecular gas, 50% of them being young ($<$ 5 Myr) and 30% being older ($>$ 10 Myr). The opposite happens to the West, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region $\sim$10 Myr ago and dispersed the molecular gas, while a second, localized episode ($<$ 5 Myr) took place in the regions where molecular gas is still present.
We have acquired radio continuum data between 70\,MHz and 48\,GHz for a sample of 19 southern starburst galaxies at moderate redshifts ($0.067 < z < 0.227$) with the aim of separating synchrotron and free-free emission components. Using a Bayesian framework we find the radio continuum is rarely characterised well by a single power law, instead often exhibiting low frequency turnovers below 500\,MHz, steepening at mid-to-high frequencies, and a flattening at high frequencies where free-free emission begins to dominate over the synchrotron emission. These higher order curvature components may be attributed to free-free absorption across multiple regions of star formation with varying optical depths. The decomposed synchrotron and free-free emission components in our sample of galaxies form strong correlations with the total-infrared bolometric luminosities. Finally, we find that without accounting for free-free absorption with turnovers between 90 to 500\,MHz the radio-continuum at low frequency ($\nu < 200$\,MHz) could be overestimated by upwards of a factor of twelve if a simple power law extrapolation is used from higher frequencies. The mean synchrotron spectral index of our sample is constrained to be $\alpha=-1.06$, which is steeper then the canonical value of $-0.8$ for normal galaxies. We suggest this may be caused by an intrinsically steeper cosmic ray distribution.
Motivated by recent observational constraints on dust reprocessed emission in star forming galaxies at $z\sim 6$ and above we use the very-large cosmological hydrodynamical simulation \bluetides\ to explore predictions for the amount of dust obscured star formation in the early Universe ($z>8$). \bluetides\ matches current observational constraints on both the UV luminosity function and galaxy stellar mass function and predicts that approximately $90\%$ of the star formation in high-mass ($M_{*}>10^{10}\,{\rm M_{\odot}}$) galaxies at $z=8$ is already obscured by dust. The relationship between dust attenuation and stellar mass predicted by \bluetides\ is consistent with that observed at lower redshift. However, observations of several individual objects at $z>6$ are discrepant with the predictions, though it is possible their uncertainties may have been underestimated. We find that the predicted surface density of $z\ge 8$ sub-mm sources is below that accessible to current {\em Herschel}, SCUBA-2, and ALMA sub-mm surveys. However, as ALMA continues to accrue additional surface area the population of $z>8$ dust-obscured galaxies may become accessible in the near future.
We present a catalog of extragalactic proper motions created using archival VLBI data and our own VLBA astrometry. The catalog contains 713 proper motions, with average uncertainties of ~ 24 muas/yr, including 40 new or improved proper motion measurements using relative astrometry with the VLBA. The observations were conducted in X-band and yielded positions with uncertainties ~ 70 muas. We add 10 new redshifts using spectroscopic observations taken at Apache Point Observatory and Gemini North. With the VLBA Extragalactic Proper Motion Catalog, we detect the secular aberration drift - the apparent motion of extragalactic objects caused by the solar system's acceleration around the Galactic center - at a 6.3 sigma significance. We model the aberration drift as a spheroidal dipole, with the square root of the power equal to 4.89 +/- 0.77 muas/yr, an amplitude of 1.69 +/- 0.27 muas/yr, and an apex at (275.2 +/- 10.0 deg, -29.4 +/- 8.8 deg). Our dipole model detects the aberration drift at a higher significance than some previous studies (e.g., Titov & Lambert 2013), but at a lower amplitude than expected or previously measured. The full aberration drift may be partially removed by the no-net-rotation constraint used when measuring archival extragalactic radio source positions. Like the cosmic microwave background dipole, which is induced by the observer's motion, the aberration drift signal should be subtracted from extragalactic proper motions in order to detect cosmological proper motions, including the Hubble expansion, long-period stochastic gravitational waves, and the collapse of large-scale structure.
The extended hot X-ray emitting gaseous halo of the Milky Way has an optical depth $\sim1$ for the dominant emission lines of \ion{O}{7} and \ion{O}{8}, which are used to infer the halo properties. To improve on halo gas properties, we treat optical depth effects with a Monte-Carlo radiative transfer model, which leads to slightly steeper density profiles ($\beta \approx 0.5$) than if optical depths effects were ignored. For the preferred model where the halo is rotating on cylinders at $180$ km s$^{-1}$, independent fits to both lines lead to identical results, where the core radius is $2.5$ kpc and the turbulent component of the Doppler b parameter is $100-120$ km s$^{-1}$; the turbulent pressure is $20\%$ of the thermal pressure. The fit is improved when emission from a disk is included, with a radial scale length of $3$ kpc (assumed) and a fitted vertical scale height of approximately $1.3$ kpc. The disk component is a minor mass constituent and has low optical depth, except at low latitudes. The gaseous mass is $3-4\times10^{10}\,M_{\odot}$ within $250\,\mathrm{kpc}$, similar to our previous determinations and significantly less than the missing baryons of $1.7\times10^{11}\,M_{\odot}$.
We present mass-loss predictions from Monte Carlo radiative transfer models for helium (He) stars as a function of stellar mass, down to 2 Msun. Our study includes both massive Wolf-Rayet (WR) stars and low-mass He stars that have lost their envelope through interaction with a companion. For these low-mass He-stars we predict mass-loss rates that are an order of magnitude smaller than by extrapolation of empirical WR mass-loss rates. Our lower mass-loss rates make it harder for these elusive stripped stars to be discovered via line emission, and we should attempt to find them through alternative methods instead. Moreover, lower mass-loss rates will make it less likely that low-mass He stars provide stripped-envelope supernovae (SNe) of type Ibc. We express our mass-loss predictions as a function of L and Z, and not as a function of the He abundance, as we do not consider this physically astute given our earlier work. The exponent of the dM/dt vs. Z dependence is found to be 0.61, which is less steep than relationships derived from recent empirical atmospheric modelling. Our shallower exponent will make it more challenging to produce "heavy" black holes of order 40 Msun, as recently discovered in the gravitational wave event GW 150914, making low metallicity for these types of events even more necessary.
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