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We study the characteristics of galaxy protoclusters using the latest L-galaxies semi-analytic model. Searching for protoclusters on a scale of $\sim 10 \, \mathrm{cMpc}$ gives an excellent compromise between the completeness and purity of their galaxy populations, leads to high distinction from the field in overdensity space, and allows accurate determination of the descendant cluster mass. This scale is valid over a range of redshifts and selection criteria. We present a procedure for estimating, given a measured galaxy overdensity, the protocluster probability and its descendant cluster mass for a range of modelling assumptions, particularly taking into account the shape of the measurement aperture. This procedure produces lower protocluster probabilities compared to previous estimates using fixed size apertures. The relationship between AGN and protoclusters is also investigated, and shows significant evolution with redshift; at $z \sim 2$ the fraction of protoclusters traced by AGN is high, but the fraction of all AGN in protoclusters is low, whereas at $z \geqslant 5$ the fraction of protoclusters containing AGN is low, but most AGN are in protoclusters. We also find indirect evidence for the emergence of a passive sequence in protoclusters at $z \sim 2$, and note that a significant fraction of all galaxies reside in protoclusters at $z \geqslant 2$, particularly the most massive.
The physical processes driving the chemical evolution of galaxies in the last $\sim 11\, \rm{Gyr}$ cannot be understood without directly probing the dust-obscured phase of star-forming galaxies and active galactic nuclei. This phase, hidden to optical tracers, represents the bulk of star formation and black hole accretion activity in galaxies at $1 < z < 3$. Spectroscopic observations with a cryogenic infrared (IR) observatory like SPICA will be sensitive enough to peer through the dust-obscured regions of galaxies and access the rest-frame mid- to far-IR range in galaxies at high-$z$. This wavelength range contains a unique suite of spectral lines and dust features that serve as proxies for the abundances of heavy elements and the dust composition, providing tracers with a feeble response to both extinction and temperature. In this work, we investigate how SPICA observations could be exploited to understand key aspects in the chemical evolution of galaxies: the assembly of nearby galaxies based on the spatial distribution of heavy element abundances, the global content of metals in galaxies reaching the knee of the luminosity function up to $z \sim 3$, and the dust composition of galaxies at high-$z$. Possible synergies with facilities available in the late 2020s are also discussed.
We introduce xCOLD GASS, a legacy survey providing a census of molecular gas in the local Universe. Building upon the original COLD GASS survey, we present here the full sample of 532 galaxies with CO(1-0) measurements from the IRAM-30m telescope. The sample is mass-selected in the redshift interval $0.01<z<0.05$ from SDSS, and therefore representative of the local galaxy population with M$_{\ast}>10^9$M$_{\odot}$. The CO(1-0) flux measurements are complemented by observations of the CO(2-1) line with both the IRAM-30m and APEX telescopes, HI observations from Arecibo, and photometry from SDSS, WISE and GALEX. Combining the IRAM and APEX data, we find that the CO(2-1) to CO(1-0) luminosity ratio for integrated measurements is $r_{21}=0.79\pm0.03$, with no systematic variations across the sample. The CO(1-0) luminosity function is constructed and best fit with a Schechter function with parameters {$L_{\mathrm{CO}}^* = (7.77\pm2.11) \times 10^9\,\mathrm{K\,km\,s^{-1}\, pc^{2}}$, $\phi^{*} = (9.84\pm5.41) \times 10^{-4} \, \mathrm{Mpc^{-3}}$ and $\alpha = -1.19\pm0.05$}. With the sample now complete down to stellar masses of $10^9$M$_{\odot}$, we are able to extend our study of gas scaling relations and confirm that both molecular gas fraction and depletion timescale vary with specific star formation rate (or offset from the star-formation main sequence) much more strongly than they depend on stellar mass. Comparing the xCOLD GASS results with outputs from hydrodynamic and semi-analytic models, we highlight the constraining power of cold gas scaling relations on models of galaxy formation.
Prior high angular resolution spectroscopic observations of the Low-ionization nuclear emission-line region (Liner) in NGC 3998 obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST) revealed a rich UV-visible spectrum consisting of broad permitted and broad forbidden emission lines. The photoionization code XSTAR is employed together with reddening-insensitive emission line diagnostics to constrain a dynamical model for the broad-line region (BLR) in NGC 3998. The BLR is modelled as a large H$^+$ region ${\sim}$ 7 pc in radius consisting of dust-free, low density ${\sim}$ 10$^4$ cm$^{-3}$, low metallicity ${\sim}$ 0.01 $Z/Z_\odot$ gas. Modelling the shape of the broad H${\alpha}$ emission line significantly discriminates between two independent measures of the black hole mass, favouring the estimate of de Francesco et al. (2006). Interpreting the broad H${\alpha}$ emission line in terms of a steady-state spherically symmetric inflow leads to a mass inflow rate of 1.4 ${\times}$ 10$^{-2}$ M$_\odot$/yr, well within the present uncertainty of calculations that attempt to explain the observed X-ray emission in terms of an advection-dominated accretion flow (ADAF). Collectively, the model provides an explanation for the shape of the H${\alpha}$ emission line, the relative intensities and luminosities for the H Balmer, [O III], and potentially several of the broad UV emission lines, as well as refining the initial conditions needed for future modelling of the ADAF.
IR spectroscopy in the range 12-230 micron with the SPace IR telescope for Cosmology and Astrophysics (SPICA) will reveal the physical processes that govern the formation and evolution of galaxies and black holes through cosmic time, bridging the gap between the James Webb Space Telescope (JWST) and the new generation of Extremely Large Telescopes (ELTs) at shorter wavelengths and the Atacama Large Millimeter Array (ALMA) at longer wavelengths. SPICA, with its 2.5-m telescope actively-cooled to below 8K, will obtain the first spectroscopic determination, in the mid-IR rest-frame, of both the star-formation rate and black hole accretion rate histories of galaxies, reaching lookback times of 12 Gyr, for large statistically significant samples. Densities, temperatures, radiation fields and gas-phase metallicities will be measured in dust-obscured galaxies and active galactic nuclei (AGN), sampling a large range in mass and luminosity, from faint local dwarf galaxies to luminous quasars in the distant Universe. AGN and starburst feedback and feeding mechanisms in distant galaxies will be uncovered through detailed measurements of molecular and atomic line profiles. SPICA's large-area deep spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for unbiased samples of tens of thousands of galaxies, out to redshifts of z~6. Furthermore, SPICA spectroscopy will uncover the most luminous galaxies in the first few hundred million years of the Universe, through their characteristic dust and molecular hydrogen features.
We present detailed image analysis of rest-frame optical images of 235 low-redshift ($z \leq$ 0.35) type 1 active galactic nuclei (AGNs) observed with the Hubble Space Telescope. The high-resolution images enable us to perform rigorous two-dimensional image modeling to decouple the luminous central point source from the host galaxy, which, when warranted, is further decomposed into its principal structural components (bulge, bar, and disk). In many cases, care must be taken to account for structural complexities such as spiral arms, tidal features, and overlapping or interacting companion galaxies. We employ Fourier modes to characterize the degree of asymmetry of the light distribution of the stars, as a quantitative measure of morphological distortion due to interactions or mergers. We examine the dependence of the physical parameters of the host galaxies on the properties of the AGNs, namely radio-loudness and the width of the broad emission lines. In accordance with previous studies, narrow-line (H$\beta$ FWHM $\leq 2000$ km~s$^{-1}$) type 1 AGNs, in contrast to their broad-line (H$\beta$ FWHM $> 2000$ km~s$^{-1}$) counterparts, are preferentially hosted in later type, lower luminosity galaxies, which have a higher incidence of pseudo-bulges, are more frequently barred, and are less morphologically disturbed. This suggests narrow-line type 1 AGNs experienced a more quiescent evolutionary history driven primarily by internal secular evolution instead of external dynamical perturbations. The fraction of AGN hosts showing merger signatures is larger for more luminous sources. Radio-loud AGNs generally preferentially live in earlier type (bulge-dominated), more massive hosts, although a minority of them appears to contain a significant disk component. We do not find convincing evidence for enhanced merger signatures in the radio-loud population.
ALMA [CII] line and continuum observations of five redshift z>6 quasars are presented. This sample was selected to probe lower black hole mass quasars than most previous studies. We find a wide dispersion in properties with CFHQS J0216-0455, a low-luminosity quasar with absolute magnitude M_1450=-22.2, remaining undetected implying a limit on the star formation rate in the host galaxy of <10 solar masses per year, whereas other host galaxies have star formation rates up to hundreds of solar masses per year. Two other quasars have particularly interesting properties. VIMOS2911 is one of the least luminous z>6 quasars known with M_1450=-23.1, yet its host galaxy is experiencing a very powerful starburst. PSO J167-13 has a broad and luminous [CII] line and a neighbouring galaxy a projected distance of 5kpc away that is also detected in the [CII] line and continuum. Combining with similar observations from the literature, we study the ratio of [CII] line to far-infrared luminosity finding this ratio increases at high-redshift at a fixed far-infrared luminosity, likely due to lower dust content, lower metallicity and/or higher gas masses. We compile a sample of 21 high-redshift quasars with dynamical masses and investigate the relationship between black hole mass and dynamical mass. The new observations presented here reveal dynamical masses consistent with the relationship defined by local galaxies. However, the full sample shows a very wide scatter across the black hole mass - dynamical mass plane, whereas both the local relationship and simulations of high-redshift quasars show a much lower dispersion in dynamical mass.
We have used the Submillimeter Array at 860$\,\mu$m to observe the brightest SCUBA-2 sources in 4$\,$deg$^{2}$ of the Cosmology Legacy Survey. We have targeted 75 of the brightest single-dish SCUBA-2 850$\,\mu$m sources down to $S_{850}\,{\approx}\,8\,$mJy, achieving an average synthesized beam of 2.4$^{\prime\prime}$ and an average rms of $\sigma_{860}\,{=}\,1.5\,$mJy in our primary beam-corrected maps. We searched our maps for $4\sigma$ peaks, corresponding to $S_{860}\,{\gtrsim}\,6\,$mJy sources, and detected 59 single galaxies and three pairs of galaxies. We include in our study 28 archival observations, bringing our sample size to 103 bright single-dish submillimetre sources with interferometric follow-up. We compute the cumulative and differential number counts of our sample, finding them to overlap with previous single-dish survey number counts within the uncertainties, although our cumulative number count is systematically lower than the parent SCUBA-2 cumulative number count by $24\,{\pm}\,6$ per cent between 11 and 15$\,$mJy. We estimate the probability that a ${\gtrsim}\,10\,$mJy single-dish submillimetre source resolves into two or more galaxies with similar flux densities, causing a significant change in the number counts, to be about 15 per cent. Assuming the remaining 85 per cent of the targets are ultra-luminous starburst galaxies between $z\,{=}\,2$-3, we find a likely volume density of ${\gtrsim}\,400\,$M$_{\odot}\,$yr$^{-1}$ sources to be ${\sim}\,3^{+0.7}_{-0.6}\,{\times}\,10^{-7}\,$Mpc$^{-3}$. We show that the descendants of these galaxies could be ${\gtrsim}\,4\,{\times}\,10^{11}\,$M$_{\odot}$ local quiescent galaxies, and that about 10 per cent of their total stellar mass would have formed during these short bursts of star-formation.
We investigate star formation occurring in idealised giant molecular clouds, comparing structures that evolve in isolation versus those undergoing a collision. Two different collision speeds are investigated and the impact of photoionising radiation from the stars is determined. We find that a colliding system leads to more massive star formation both with and without the addition of feedback, raising overall star formation efficiencies (SFE) by a factor of 10 and steepening the high-mass end of the stellar mass function. This rise in SFE is due to increased turbulent compression during the cloud collision. While feedback can both promote and hinder star formation in the isolated system, it increases the SFE by approximately 1.5 times in the colliding case when the thermal speed of the resulting HII regions matches the shock propagation speed in the collision.
Our current knowledge of star formation and accretion luminosity at high-redshift (z>3-4), as well as the possible connections between them, relies mostly on observations in the rest-frame ultraviolet (UV), which are strongly affected by dust obscuration. Due to the lack of sensitivity of past and current infrared (IR) instrumentation, so far it has not been possible to get a glimpse into the early phases of the dust-obscured Universe. Among the next generation of IR observatories, SPICA, observing in the 12-350 micron range, will be the only facility that can enable us to make the required leap forward in understanding the obscured star-formation rate and black-hole accretion rate densities (SFRD and BHARD, respectively) with respect to what Spitzer and Herschel achieved in the mid- and far-IR at z<3. In particular, SPICA will have the unique ability to trace the evolution of the obscured SFRD and BHARD over cosmic time, from the peak of their activity back to the reionisation epoch (i.e., 3<z<6-7), where its predecessors had severe limitations. Here we discuss the potential of both deep and shallow photometric surveys performed with the SPICA mid-IR instrument (SMI), enabled by the very low level of impact of dust obscuration in a band centred at 34 micron. These unique unbiased photometric surveys that SPICA will perform will be followed up by observations both with the SPICA spectrometers and with other facilities at shorter and longer wavelengths, with the aim to fully characterise the evolution of AGNs and star-forming galaxies after re-ionisation.
A far-infrared observatory such as the {\it SPace Infrared telescope for Cosmology and Astrophysics} ({\it SPICA}), with its unprecedented spectroscopic sensitivity, would unveil the role of feedback in galaxy evolution during the last $\sim10$ Gyr of the Universe ($z=1.5-2$), through the use of far- and mid-infrared molecular and ionic fine structure lines that trace outflowing and infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni line shapes and absorption blueshifted wings in molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of ionized gas. We quantify the detectability of galaxy-scale massive molecular and ionized outflows as a function of redshift in AGN-dominated, starburst-dominated, and main-sequence galaxies, explore the detectability of metal-rich inflows in the local Universe, and describe the most significant synergies with other current and future observatories that will measure feedback in galaxies via complementary tracers at other wavelengths.
Luminous radio sources are thought to lie in galaxy clusters or proto-clusters. The complete sample of 64 high-redshift 3C sources at $1<z<2.5$ has been mapped with the Spitzer Space Telescope. The IRAC $3.6\mu$m and $4.5\mu$m 5-$\sigma$ detection limit of $4\mu$Jy (22.4 AB mag) allows us to search for the brightest candidate cluster member galaxies associated with the 3C sources. To remove the contamination of foreground stars and galaxies along the lines of sight toward the 3C sources we apply color cuts: removed sources satisfy either the IRAC1/2 cut $[3.6] - [4.5] < -0.3$ or the Pan-STARRS/IRAC cut $i - [4.5] < 0.5$ if detected by Pan-STARRS. For both selection methods, about half of the 3C radio sources show significant overdensities ($>3\sigma$) within 30" ($\sim$250 kpc) projected distance from the radio source compared to the surrounding galaxy densities measured in the $50''-120''$ annulus. The Pan-STARRS/IRAC cut reveals higher average overdensities than the IRAC1/2 cut and also a decline of overdensities at $z>1.4$. To infer the nature of the cluster members, we rerun the analysis using a stronger IRAC1/2 cut $[3.6] - [4.5] < -0.1$ which removes $1<z<1.4$ passive ellipticals but not star-forming galaxies. For the strong cut, the overdensities, on average, completely disappear at $1<z<1.4$. We therefore suggest that the 4.5$\mu$m detected cluster member galaxies are mainly passive ellipticals.
We have measured the absolute proper motion of the Sextans dwarf spheroidal galaxy using Subaru Suprime-Cam images taken at three epochs, with a time baseline of ~ 10 years. We astrometrically calibrate each epoch by constructing distortion-correction maps from the best available Subaru Suprime-Cam dithered data sets and from Gaia DR1 positions. The magnitude limit of the proper-motion study is V ~ 24. The area covered is 26.7 x 23.3 arcmin, which is still within the core radius of Sextans. The derived proper motion is (mu_a, mu_d) = (-0.409 +/- 0.050, -0.047 +/- 0.058) mas/yr. The direction of motion is perpendicular to the major axis of the galaxy. Our measurement, combined with radial velocity and distance from the literature, implies a low eccentricity orbit, with a moderate inclination to the Galactic plane, and a period of 3 Gyr. Sextans is now some 0.4 Gyr away from its pericenter ( r_peri ~ 75 kpc), moving toward its apocenter (r_apo ~ 132 kpc). Its orbit is inconsistent with membership to the vast polar structure of Galactic satellites.
We use CARMA 3mm continuum and molecular lines (NH2D, N2H+, HCO+, HCN and CS) at ~1000 au resolution to characterize the structure and kinematics of the envelope surrounding the deeply embedded first core candidate Per-Bolo 58. The line profile of the observed species shows two distinct peaks separated by 0.4-0.6 km/s, most likely arising from two different optically thin velocity components rather than the product of self-absorption in an optically thick line. The two velocity components, each with a mass of ~0.5-0.6 Msun, overlap spatially at the position of the continuum emission, and produce a general gradient along the outflow direction. We investigate whether these observations are consistent with infall in a turbulent and magnetized envelope. We compare the morphology and spectra of the N2H+(1-0) with synthetic observations of an MHD simulation that considers the collapse of an isolated core that is initially perturbed with a turbulent field. The proposed model matches the data in the production of two velocity components, traced by the isolated hyperfine line of the N2H+(1-0) spectra and shows a general agreement in morphology and velocity field. We also use large maps of the region to compare the kinematics of the core with that of the surrounding large-scale filamentary structure and find that accretion from the large-scale filament could also explain the complex kinematics exhibited by this young dense core.
The Binary Population and Spectral Synthesis (BPASS) suite of binary stellar evolution models and synthetic stellar populations provides a framework for the physically motivated analysis of both the integrated light from distant stellar populations and the detailed properties of those nearby. We present a new version 2.1 data release of these models, detailing the methodology by which BPASS incorporates binary mass transfer and its effect on stellar evolution pathways, as well as the construction of simple stellar populations. We demonstrate key tests of the latest BPASS model suite demonstrating its ability to reproduce the colours and derived properties of resolved stellar populations, including well- constrained eclipsing binaries. We consider observational constraints on the ratio of massive star types and the distribution of stellar remnant masses. We describe the identification of supernova progenitors in our models, and demonstrate a good agreement to the properties of observed progenitors. We also test our models against photometric and spectroscopic observations of unresolved stellar populations, both in the local and distant Universe, finding that binary models provide a self-consistent explanation for observed galaxy properties across a broad redshift range. Finally, we carefully describe the limitations of our models, and areas where we expect to see significant improvement in future versions.
We present the results of targeted observations and a survey of 1612-, 1665-, and 1667-MHz circumstellar OH maser emission from asymptotic giant branch (AGB) stars and red supergiants (RSGs) in the Small Magellanic Cloud (SMC), using the Parkes and Australia Telescope Compact Array radio telescopes. No clear OH maser emission has been detected in any of our observations targeting luminous, long-period, large-amplitude variable stars, which have been confirmed spectroscopically and photometrically to be mid- to late-M spectral type. These observations have probed 3 - 4 times deeper than any OH maser survey in the SMC. Using a bootstrapping method with LMC and Galactic OH/IR star samples and our SMC observation upper limits, we have calculated the likelihood of not detecting maser emission in any of the two sources considered to be the top maser candidates to be less than 0.05%, assuming a similar pumping mechanism as the LMC and Galactic OH/IR sources. We have performed a population comparison of the Magellanic Clouds and used Spitzer IRAC and MIPS photometry to confirm that we have observed all high luminosity SMC sources that are expected to exhibit maser emission. We suspect that, compared to the OH/IR stars in the Galaxy and LMC, the reduction in metallicity may curtail the dusty wind phase at the end of the evolution of the most massive cool stars. We also suspect that the conditions in the circumstellar envelope change beyond a simple scaling of abundances and wind speed with metallicity.
Star formation in magnetically subcritical clouds is investigated using a three-dimensional non-ideal magneto-hydrodynamics simulation. Since rapid cloud collapse is suppressed until the magnetic flux is sufficiently removed from the initially magnetically subcritical cloud by ambipolar diffusion, it takes > 5-10t_ff to form a protostar, where t_ff is the freefall timescale of the initial cloud. The angular momentum of the star forming cloud is efficiently transferred to the interstellar medium before the rapid collapse begins, and the collapsing cloud has a very low angular momentum. Unlike the magnetically supercritical case, no large-scale low-velocity outflow appears in such a collapsing cloud due to the short lifetime of the first core. Following protostar formation, a very weak high-velocity jet, which has a small momentum and might disappear at a later time, is driven near the protostar, while the circumstellar disc does not grow during the early mass accretion phase. The results show that the star formation process in magnetically subcritical clouds is qualitatively different from that in magnetically supercritical clouds.
Using the HPC ressources of the state of Baden-W\"urttemberg, we modelled for the first time the luminous burst from a young massive star by accretion of material from its close environment. We found that the surroundings of young massive stars are shaped as a clumpy disk whose fragments provoke outbursts once they fall onto the protostar and concluded that similar strong luminous events observed in high-mass star forming regions may be a signature of the presence of such disks.
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We present the ionized gas properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that show an extreme optical/IR color, $(i - [22])_{\rm AB} > 7.0$, selected with the Sloan Digital Sky Survey (SDSS) and Wide-field Infrared Survey Explorer (WISE). For 36 IR-bright DOGs that show [OIII]$\lambda$5007 emission in the SDSS spectra, we performed a detailed spectral analysis to investigate their ionized gas properties. In particular, we measured the velocity offset (the velocity with respect to the systemic velocity measured from the stellar absorption lines) and the velocity dispersion of the [OIII] line. We found that the derived velocity offset and dispersion of most IR-bright DOGs are larger than those of Seyfert 2 galaxies (Sy2s) at $z < 0.3$, meaning that the IR-bright DOGs show relatively strong outflows compared to Sy2s. This can be explained by the difference of IR luminosity contributed from active galactic nucleus, $L_{\rm IR}$ (AGN), because we found that (i) $L_{\rm IR}$ (AGN) correlates with the velocity offset and dispersion of [OIII] and (ii) our IR-bright DOGs sample has larger $L_{\rm IR}$ (AGN) than Sy2s. Nevertheless, the fact that about 75% IR-bright DOGs have a large ($>$ 300 km s$^{-1}$) velocity dispersion, which is a larger fraction compared to other AGN populations, suggests that IR-bright DOGs are good laboratories to investigate AGN feedback. The velocity offset and dispersion of [OIII] and [NeIII]$\lambda$3869 are larger than those of [OII]$\lambda$3727, which indicates that the highly ionized gas tends to show more stronger outflows.
We present a semi-analytic model of star formation in the early universe, beginning with the first metal-free stars. By employing a completely feedback-limited star formation prescription, stars form at maximum efficiency until the self-consistently calculated feedback processes halt formation. We account for a number of feedback processes including a meta-galactic Lyman-Werner background, supernovae, photoionization, and chemical feedback. Halos are evolved combining mass accretion rates found through abundance matching with our feedback-limited star formation prescription, allowing for a variety of Population III (Pop III) initial mass functions (IMFs). We find that, for a number of models, massive Pop III star formation can continue on until at least $z \sim 20$ and potentially past $z \sim 6$ at rates of around $10^{-4}$ to $10^{-5}$ M$_\odot$ yr$^{-1}$ Mpc$^{-3}$, assuming these stars form in isolation. At this point Lyman-Werner feedback pushes the minimum halo mass for star formation above the atomic cooling threshold, cutting off the formation of massive Pop III stars. We find that, in most models, Pop II and Pop III star formation co-exist over cosmological time-scales, with the total star formation rate density and resulting radiation background strongly dominated by the former before Pop III star formation finally ends. These halos form at most $\sim 10^3$ M$_\odot$ of massive Pop III stars during this phase and typically have absolute magnitudes in the range of $M_\text{AB} = -5 $ to $ -10$. We also briefly discuss how future observations from telescopes such as JWST or WFIRST and 21-cm experiments may be able to constrain unknown parameters in our model such as the IMF, star formation prescription, or the physics of massive Pop III stars.
We investigate the effects of Population III stars on the sky-averaged 21-cm background radiation, which traces the collective emission from all sources of ultraviolet and X-ray photons before reionization is complete. While UV photons from PopIII stars can in principle shift the onset of radiative coupling of the 21-cm transition -- and potentially reionization -- to early times, we find that the remnants of PopIII stars are likely to have a more discernible impact on the 21-cm signal than PopIII stars themselves. The X-rays from such sources preferentially heat the IGM at early times, which elongates the epoch of reheating and results in a more gradual transition from an absorption signal to emission. This gradual heating gives rise to broad, asymmetric wings in the absorption signal, which stand in contrast to the relatively sharp, symmetric signals that arise in models treating PopII sources only. A stronger signature of PopIII, in which the position of the absorption minimum becomes inconsistent with PopII-only models, requires extreme star-forming events that may not be physically plausible, lending further credence to predictions of relatively high frequency absorption troughs, $\nu_{\min} \sim 100$ MHz. As a result, though the trough location alone may not be enough to indicate the presence of PopIII, the asymmetric wings should arise even if only a few PopIII stars form in each halo before the transition to PopII star formation occurs, provided that the PopIII IMF is sufficiently top-heavy and at least some PopIII stars form in binaries.
We present N-body simulations of a Sagittarius-like dwarf spheroidal galaxy (Sgr) that follow its orbit about the Milky Way (MW) since its first crossing of the Galaxy's virial radius to the present day. As Sgr orbits around the MW, it excites vertical oscillations, corrugating and flaring the Galactic stellar disc. These responses can be understood by a two-phase picture in which the interaction is first dominated by torques from the wake excited by Sgr in the MW dark halo before transitioning to tides from Sgr's direct impact on the disc at late times. We show for the first time that a massive Sgr model simultaneously reproduces the locations and motions of arc-like over densities, such as the Monoceros Ring and the Triangulum Andromeda stellar clouds, that have been observed at the extremities of the disc, while also satisfying the solar neighbourhood constraints on the vertical structure and streaming motions of the disc. In additional simulations, we include the Large Magellanic Cloud (LMC) self consistently with Sgr. The LMC introduces coupling through constructive and destructive interference, but no new corrugations. In our models, the excitation of the current structure of the outer disk can be traced to interactions as far back as 6-7 Gyr ago (corresponding to $z\leq1$). Given the apparently quiescent accretion history of the MW over this timescale, this places Sgr as the main culprit behind the vertical oscillations of the disc and the last major accretion event for the Galaxy with the capacity to modulate its chemodynamical structure.
The optical spectroscopic and radio interferometric HI 21 cm-line observations of the blue compact dwarf galaxy Mrk 22 are presented. The Wolf-Rayet (WR) emission line features corresponding to high ionization lines of HeII $\lambda$4686 and CIV $\lambda$5808 from young massive stars are detected. The ages of two prominent star forming regions in the galaxy are estimated as $\sim$10 Myr and $\sim$ 4 Myr. The galaxy has non-thermal radio deficiency, which also indicates a young star-burst and lack of supernovae events from the current star formation activities, consistent with the detection of WR emission lines features. A significant N/O enrichment is seen in the fainter star forming region. The gas-phase metallicities [12 + log(O/H)] for the bright and faint regions are estimated as 7.98$\pm$0.07 and 7.46$\pm$0.09 respectively. The galaxy has a large diffuse HI envelop. The HI images reveal disturbed gas kinematics and HI clouds outside the optical extent of the galaxy, indicating recent tidal interaction or merger in the system. The results strongly indicate that Mrk 22 is undergoing a chemical and morphological evolution due to ongoing star formation, most likely triggered by a merger.
The role of the cosmic web in shaping galaxy properties is investigated in the GAMA spectroscopic survey in the redshift range $0.03 \leq z \leq 0.25$. The stellar mass, $u - r$ dust corrected colour and specific star formation rate (sSFR) of galaxies are analysed as a function of their distances to the 3D cosmic web features, such as nodes, filaments and walls, as reconstructed by DisPerSE. Significant mass and type/colour gradients are found for the whole population, with more massive and/or passive galaxies being located closer to the filament and wall than their less massive and/or star-forming counterparts. Mass segregation persists among the star-forming population alone. The red fraction of galaxies increases when closing in on nodes, and on filaments regardless of the distance to nodes. Similarly, the star-forming population reddens (or lowers its sSFR) at fixed mass when closing in on filament, implying that some quenching takes place. Comparable trends are also found in the state-of-the-art hydrodynamical simulation Horizon-AGN. These results suggest that on top of stellar mass and large-scale density, the traceless component of the tides from the anisotropic large-scale environment also shapes galactic properties. An extension of excursion theory accounting for filamentary tides provides a qualitative explanation in terms of anisotropic assembly bias: at a given mass, the accretion rate varies with the orientation and distance to filaments. It also explains the absence of type/colour gradients in the data on smaller, non-linear scales.
The 30 Doradus Nebula in the Large Magellanic Cloud (LMC) contains the massive starburst cluster NGC 2070 with a massive and probably younger stellar sub clump at its center: R136. It is not clear how such a massive inner cluster could form several million years after the older stars in NGC 2070, given that stellar feedback is usually thought to expel gas and inhibit further star formation. Using the recently developed 1D feedback scheme WARPFIELD to scan a large range of cloud and cluster properties, we show that an age offset of several million years between the stellar populations is in fact to be expected given the interplay between feedback and gravity in a giant molecular cloud (GMC) with a density $\gtrsim 500$ cm$^{-3}$ due to re-accretion of gas onto the older stellar population. Neither capture of field stars nor gas retention inside the cluster have to be invoked in order to explain the observed age offset in NGC 2070 as well as the structure of the interstellar medium (ISM) around it.
Recent literature suggests that there are two modes through which galaxies grow their stellar mass - a normal mode characterized by quasi-steady star formation, and a highly efficient starburst mode possibly triggered by stochastic events such as galaxy mergers. While these differences are established for extreme cases, the population of galaxies in-between these two regimes is poorly studied and it is not clear where the transition between these two modes of star formation occurs. We utilize ALMA observations of the CO J=3-2 line luminosity in a sample of 20 infrared luminous galaxies that lie in the intermediate range between normal and starburst galaxies at z ~ 0.25-0.6 in the COSMOS field to examine the gas content and star formation efficiency of these galaxies. We compare these quantities to the galaxies' deviation from the well-studied "main sequence" correlation between star formation rate and stellar mass (MS) and find that at log($SFR/SFR_{MS}$) < 0.6, a galaxy's distance to the main sequence is mostly driven by increased gas content, and not a more efficient star formation process.
We present a multiwavelength investigation of the HII region G25.8700+0.1350, located in the inner part of the Galaxy. In radio continuum emission, the region is seen as a bright arc-shaped structure. An analysis of the HI line suggests that G25.8700+0.1350 lies at a distance of 6.5 kpc. The ionized gas is bordered by a photodissociation region which is encircled by a molecular structure where four molecular clumps are detected. At infrared wavelengths, the region is also very conspicuous. Given the high level of visual absorption in the region, the exciting stars should be searched for in the infrared band. In this context, we found in the literature one Wolf-Rayet and one red supergiant which, together with 37 2MASS sources candidates to be O-type stars, could be related to the origin of G25.8700+0.1350. Finally, as expanding HII regions are hypothesized to trigger star formation, we used different infrared point source catalogues to search for young stellar object candidates (cYSOs). A total of 45 cYSOs were identified projected onto the molecular clouds.
${\bf Aim:}$ To test the hypothesis that radiation pressure from star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process. ${\bf Methods:}$ We perform multi-frequency, 3D, RT calculations including scattering, absorption, and re-emission to longer wavelengths for clouds with masses of $10^4$-$10^7\,$M$_{\odot}$, with embedded clusters and a star formation efficiencies of 0.009%-91%, and varying maximum grain sizes up to 200$\,\mu$m. We calculate the ratio between radiative force and gravity to determine whether radiation pressure can disrupt clouds. ${\bf Results:}$ We find that radiation acting on dust almost never disrupts star-forming clouds. UV and optical photons to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by at thermal wavelengths. As the cloud is typically optically thin to far-IR radiation, it promptly escapes, depositing little momentum. The resulting spectrum is more narrowly peaked than the corresponding Planck function with an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm, the resulting radiative force is even smaller than for the corresponding single-temperature black body. The force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or starbust conditions. For unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity. ${\bf Conclusions:}$ We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star-formation process on either local or global scales.
We present the MUSE Hubble Ultra Deep Survey, a mosaic of nine MUSE fields covering 90\% of the entire HUDF region with a 10-hour deep exposure time, plus a deeper 31-hour exposure in a single 1.15 arcmin2 field. The improved observing strategy and advanced data reduction results in datacubes with sub-arcsecond spatial resolution (0.65 arcsec at 7000 A) and accurate astrometry (0.07 arcsec rms). We compare the broadband photometric properties of the datacubes to HST photometry, finding a good agreement in zeropoint up to mAB=28 but with an increasing scatter for faint objects. We have investigated the noise properties and developed an empirical way to account for the impact of the correlation introduced by the 3D drizzle interpolation. The achieved 3 sigma emission line detection limit for a point source is 1.5 and 3.1 10-19 erg.s-1.cm-2 for the single ultra-deep datacube and the mosaic, respectively. We extracted 6288 sources using an optimal extraction scheme that takes the published HST source locations as prior. In parallel, we performed a blind search of emission line galaxies using an original method based on advanced test statistics and filter matching. The blind search results in 1251 emission line galaxy candidates in the mosaic and 306 in the ultradeep datacube, including 72 sources without HST counterparts (mAB>31). In addition 88 sources missed in the HST catalog but with clear HST counterparts were identified. This data set is the deepest spectroscopic survey ever performed. In just over 100 hours of integration time, it provides nearly an order of magnitude more spectroscopic redshifts compared to the data that has been accumulated on the UDF over the past decade. The depth and high quality of these datacubes enables new and detailed studies of the physical properties of the galaxy population and their environments over a large redshift range.
We combine inferred galaxy properties from a semi-analytic galaxy evolution model incorporating dark matter halo merger trees with new estimates of supernova and gamma ray burst rates as a function of metallicity from stellar population synthesis models incorporating binary interactions. We use these to explore the stellar mass fraction of galaxies irradiated by energetic astrophysical transients and its evolution over cosmic time, and thus the fraction which is potentially habitable by life like our own. We find that 18 per cent of the stellar mass in the Universe is likely to have been irradiated within the last 260 Myr, with GRBs dominating that fraction. We do not see a strong dependence of irradiated stellar mass fraction on stellar mass or richness of the galaxy environment. We consider a representative merger tree as a Local Group analogue, and find that there are galaxies at all masses which have retained a high habitable fraction (>50 per cent) over the last 6 Gyr, but also that there are galaxies at all masses where the merger history and associated star formation have rendered galaxies effectively uninhabitable. This illustrates the need to consider detailed merger trees when evaluating the cosmic evolution of habitability.
We present the largest catalogue of HI single dish observations of isolated galaxies to date and the corresponding HI scaling relations, as part of the multi-wavelength project AMIGA (Analysis of the interstellar Medium in Isolated GAlaxies). Despite numerous studies of the HI content of galaxies, no revision has been made for the most isolated galaxies since 1984. In total we have measurements or constraints on the HI masses of 844 galaxies from the Catalogue of Isolated Galaxies (CIG), obtained with our own observations at Arecibo, Effelsberg, Nancay and GBT, and spectra from the literature. Cuts are made to this sample to ensure isolation and a high level of completeness. We then fit HI scaling relations based on luminosity, optical diameter and morphology. Our regression model incorporates all the data, including upper limits, and accounts for uncertainties in both variables, as well as distance uncertainties. The scaling relation of HI mass with optical diameter is in good agreement with that of Haynes & Giovanelli 1984, but our relation with luminosity is considerably steeper. This is attributed to the large uncertainties in the luminosities, which introduce a bias when using OLS regression (used previously), and the different morphology distributions of the samples. We find that the main effect of morphology on the relations is to increase the intercept and flatten the slope towards later types. These trends were not evident in previous works due to the small number of detected early-type galaxies. The HI scaling relations of the AMIGA sample define an up-to-date metric of the HI content of almost "nurture free" galaxies. These relations allow the expected HI mass, in the absence of interactions, of a galaxy to be predicted to within 0.25 dex, and are thus suitable for use as statistical measures of the impact of interactions on the neutral gas content of galaxies. (Abridged)
As radio polarised emission from astrophysical objects traverse through foreground magnetised plasma, the physical conditions along the lines of sight are encrypted in the form of Rotation Measure (RM). We performed broadband spectro-polarimetric observations of high Rotation Measure (|RM| >~ 300 rad m-2) sources away from the Galactic plane (|b| > 10 deg) selected from the NVSS RM catalogue. The main goals are to verify the NVSS RM values, which could be susceptible to n{\pi}-ambiguity, as well as to identify the origin of the extreme RM values. We show that 40 % of our sample suffer from n{\pi}-ambiguity in the NVSS RM catalogue. There are also hints of RM variabilities over ~20 years epoch for most of our sources, as revealed by comparing the RM values of the two studies in the same frequency ranges after correcting for n{\pi}-ambiguity. At last, we demonstrate the possibility of applying QU-fitting to study the ambient media of AGNs.
Dark Matter (DM) and Modified Newtonian Dynamics (MOND) lead to different geometries for galactic rotation curves in $(g_{bar},g_{obs})$-space ($g2$-space). Here $g_{obs}$ is the total (observed) centripetal acceleration of matter in a rotationally supported galaxy and $g_{bar}$ is that from the visible (baryonic) matter distribution. DM and MOND predict closed curves, $\mathcal{C}_{DM/MOND}$, in $g2$-space where the area spanned by the DM curve is non-zero, $\mathcal{A}(\mathcal{C}_{DM})\neq 0$, whereas the area spanned by the MOND curve vanishes, $\mathcal{A}(\mathcal{C}_{MOND})=0$. Galaxies from the SPARC database\cite{SPARC} are investigated in order to determine if $\mathcal{A}(\mathcal{C}_{data})\neq 0$ in current data.
The radio continuum spectra of 14 star-forming galaxies are investigated by fitting nonthermal (synchrotron) and thermal (free-free) radiation laws. The underlying radio continuum measurements cover a frequency range of ~325 MHz to 24.5 GHz (32 GHz in case of M82). It turns out that most of these synchrotron spectra are not simple power-laws, but are best represented by a low-frequency spectrum with a mean slope alpha_nth = 0.59 +/- 0.20 (S_nu ~ nu^-alpha), and by a break or an exponential decline in the frequency range of 1 - 12 GHz. Simple power-laws or mildly curved synchrotron spectra lead to unrealistically low thermal flux densities, and/or to strong deviations from the expected optically thin free-free spectra with slope alpha_th = 0.10 in the fits. The break or cutoff energies are in the range of 1.5 - 7 GeV. We briefly discuss the possible origin of such a cutoff or break. If the low-frequency spectra obtained here reflect the injection spectrum of cosmic-ray electrons, they comply with the mean spectral index of Galactic supernova remnants. A comparison of the fitted thermal flux densities with the (foreground-corrected) Halpha fluxes yields the extinction, which increases with metallicity. The fraction of thermal emission is higher than believed hitherto, especially at high frequencies, and is highest in the dwarf galaxies of our sample, which we interpret in terms of a lack of containment in these low-mass systems, or a time effect caused by a very young starburst.
Faint star-forming galaxies at $z\sim 2-3$ can be used as alternative background sources to probe the Lyman-$\alpha$ forest in addition to quasars, yielding high sightline densities that enable 3D tomographic reconstruction of the foreground absorption field. Here, we present the first data release from the COSMOS Lyman-Alpha Mapping And Mapping Observations (CLAMATO) Survey, which was conducted with the LRIS spectrograph on the Keck-I telescope. Over an observational footprint of 0.157$\mathrm{deg}^2$ within the COSMOS field, we used 240 galaxies and quasars at $2.17<z<3.00$, with a mean comoving transverse separation of $2.37\,h^{-1}\,\mathrm{Mpc}$, as background sources probing the foreground Lyman-$\alpha$ forest absorption at $2.05<z<2.55$. The Lyman-$\alpha$ forest data was then used to create a Wiener-filtered tomographic reconstruction over a comoving volume of $3.15\,\times 10^5\,h^{-3}\,\mathrm{Mpc^3}$ with an effective smoothing scale of $2.5\,h^{-1}\,\mathrm{Mpc}$. In addition to traditional figures, this map is also presented as a virtual-reality YouTube360 video visualization and manipulable interactive figure. We see large overdensities and underdensities that visually agree with the distribution of coeval galaxies from spectroscopic redshift surveys in the same field, including overdensities associated with several recently-discovered galaxy protoclusters in the volume. This data release includes the redshift catalog, reduced spectra, extracted Lyman-$\alpha$ forest pixel data, and tomographic map of the absorption.
Protoplanetary disk mass is a key parameter controlling the process of planetary system formation. CO molecular emission is often used as a tracer of gas mass in the disk. In this study we consider the ability of CO to trace the gas mass over a wide range of disk structural parameters and search for chemical species that could possibly be used as alternative mass tracers to CO. Specifically, we apply detailed astrochemical modeling to a large set of models of protoplanetary disks around low-mass stars, to select molecules with abundances correlated with the disk mass and being relatively insensitive to other disk properties. We do not consider sophisticated dust evolution models, restricting ourselves with the standard astrochemical assumption of $0.1~\mu $m dust. We find that CO is indeed the best molecular tracer for total gas mass, despite the fact that it is not the main carbon carrier, provided reasonable assumptions about CO abundance in the disk are used. Typically, chemical reprocessing lowers the abundance of CO by a factor of 3, compared to the case of photo-dissociation and freeze-out as the only ways of CO depletion. On average only 13% C-atoms reside in gas-phase CO, albeit with variations from 2 to 30%. CO$_2$, H$_2$O and H$_2$CO can potentially serve as alternative mass tracers, the latter two being only applicable if disk structural parameters are known.
In the last decade the detection of individual massive dark matter sub-halos has been possible using potential correction formalism in strong gravitational lens imaging. Here we propose a statistical formalism to relate strong gravitational lens surface brightness anomalies to the lens potential fluctuations arising from dark matter distribution in the lens galaxy. We consider these fluctuations as a Gaussian random field in addition to the unperturbed smooth lens model. This is very similar to weak lensing formalism and we show that in this way we can measure the power spectrum of these perturbations to the potential. We test the method by applying it to simulated mock lenses of different geometries and by performing an MCMC analysis of the theoretical power spectra. This method can measure density fluctuations in early type galaxies on scales of 1-10 kpc at typical rms-levels of a percent, using a single lens system observed with the Hubble Space Telescope with typical signal-to-noise ratios obtained in a single orbit.
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We present results from the MOSFIRE Deep Evolution Field (MOSDEF) survey on broad flux from the nebular emission lines H$\alpha$, [NII], [OIII], H$\beta$, and [SII]. The sample consists of 127 star-forming galaxies at $1.37 < z < 2.61$ and 84 galaxies at $2.95 < z < 3.80$. We decompose the emission lines using narrow ($\text{FWHM} < 275 \ \text{km s}^{-1}$) and broad ($\text{FWHM} > 300 \ \text{km s}^{-1}$) Gaussian components for individual galaxies and stacks. Broad emission is detected at $>3\sigma$ in $<10$% of galaxies and the broad flux accounts for 10-70% of the total flux. We find a slight increase in broad to narrow flux ratio with mass but note that we cannot reliably detect broad emission with $\text{FWHM} < 275 \ \text{km s}^{-1}$, which may be significant at low masses. Notably, there is a correlation between higher signal-to-noise (S/N) spectra and a broad component detection indicating a S/N dependence in our ability to detect broad flux. When placed on the N2-BPT diagram ([OIII]/H$\beta$ vs. [NII]/H$\alpha$) the broad components of the stacks are shifted towards higher [OIII]/H$\beta$ and [NII]/$\alpha$ ratios compared to the narrow component. We compare the location of the broad components to shock models and find that the broad component could be due to shocks, but we do not rule out other possibilities such as the presence of an AGN. We estimate the mass loading factor (mass outflow rate/star formation rate) assuming the broad component is a photoionized outflow and find that the mass loading factor increases as a function of mass which agrees with previous studies. We show that adding emission from shocked gas to $z\sim0$ SDSS spectra shifts galaxies towards the location of $z\sim2$ galaxies on several emission line diagnostic diagrams.
We present an ultraviolet spectroscopic survey of strong H I absorbers in the intergalactic medium, probing their evolution over the last 6-7 Gyr at redshifts $0.24 \leq z \leq 0.84$. We measure column densities $N_{\rm HI} \,( {\rm cm}^{-2})$ from the pattern of Lyman-series absorption lines and flux decrement at the Lyman limit (LL) when available. We analyzed 220 H I absorbers in ultraviolet spectra of 102 active galactic nuclei (AGN) taken by the Cosmic Origins Spectrograph aboard the Hubble Space Telescope with G130M/G160M gratings (1134-1795 \AA). For 158 absorbers with $\log N_{\rm HI} \geq 15$, the mean frequency is $d {\cal N}/dz = 4.95 \pm 0.39$ over pathlength $\Delta z = 31.94$ ($0.24 \leq z \leq 0.84)$. We identify 8 Lyman Limit Systems (LLS, $\log N_{\rm HI} \geq 17.2$) and 54 partial systems (pLLS) with $16.0 \leq \log N_{\rm HI} < 17.2$. Toward 159 AGN between $0.01 < z_{\rm abs} < 0.84$ with $\Delta z \approx 48$, we find four damped Ly$\alpha$ absorbers (DLA) with $(d {\cal N}/dz)_{\rm DLA} = 0.083^{+0.066}_{-0.040}$ at $\langle z \rangle = 0.18$. The mean LLS frequency between $z = 0.24-0.48$ is $(d {\cal N}/dz)_{\rm LLS} = 0.36^{+0.20}_{-0.13}$ fitted to $N(z) = (0.25^{+0.13}_{-0.09})(1+z)^{1.14}$. For 54 pLLS we find $(d {\cal N}/dz)_{\rm pLLS} = 1.69\pm0.23$ at $\langle z \rangle = 0.39$, a frequency consistent with gaseous halo sizes $R \approx 100 h^{-1}~{\rm kpc}$ for ($0.3-3L^*$) galaxies. A maximum-likelihood analysis yields a distribution $f(N,z) = C_0 N^{-\beta} (1+z)^{\gamma}$ with $\beta = 1.48 \pm 0.05$ and $\gamma = 1.14^{+0.88}_{-0.89}$ for $15 \leq \log N_{\rm HI} \leq 17.5$. The far-UV opacity gradient is $d \tau_{\rm eff} / dz \approx (0.444)(1+z)^{1.14}$ over the range $15 \leq \log N_{\rm HI} \leq 17$, implying mean LyC optical depth $\tau_{\rm eff} \approx 0.3-0.5$ toward sources at $z = 1-2$.
We analyze the evolution of the dual AGN in ESO 509-IG066, a galaxy pair located at z=0.034 whose nuclei are separated by 11 kpc. Previous observations with XMM-Newton on this dual AGN found evidence for two moderately obscured ($N_H\sim10^{22}$ cm$^{-2}$) X-ray luminous ($L_X\sim10^{43}$ erg/s) nuclear sources. We present an analysis of subsequent Chandra, NuSTAR and Swift/XRT observations that show one source has dropped in flux by a factor of 10 between 2004 and 2011, which could be explained by either an increase in the absorbing column or an intrinsic fading of the central engine possibly due to a decrease in mass accretion. Both of these scenarios are predicted by galaxy merger simulations. The source which has dropped in flux is not detected by NuSTAR, which argues against absorption, unless it is extreme. However, new Keck/LRIS optical spectroscopy reveals a previously unreported broad H-alpha line which is highly unlikely to be visible under the extreme absorption scenario. We therefore conclude that the black hole in this nucleus has undergone a dramatic drop in accretion rate. From AO-assisted near-infrared integral-field spectroscopy of the other nucleus, we find evidence that the galaxy merger is having a direct effect on the kinematics of the gas close to the nucleus of the galaxy, providing a direct observational link between the galaxy merger and the mass accretion rate on to the black hole.
We introduce a method for modeling disk galaxies designed to take full advantage of data from integral field spectroscopy (IFS). The method fits equilibrium models to simultaneously reproduce the surface brightness, rotation and velocity dispersion profiles of a galaxy. The models are fully self-consistent 6D distribution functions for a galaxy with a Sersic-profile stellar bulge, exponential disk and parametric dark matter halo, generated by an updated version of GalactICS. By creating realistic flux-weighted maps of the kinematic moments (flux, mean velocity and dispersion), we simultaneously fit photometric and spectroscopic data using both maximum-likelihood and Bayesian (MCMC) techniques. We apply the method to a GAMA spiral galaxy (G79635) with kinematics from the SAMI Galaxy Survey and deep $g$- and $r$-band photometry from the VST-KiDS survey, comparing parameter constraints with those from traditional 2D bulge-disk decomposition. Our method returns broadly consistent results for shared parameters, while constraining the mass-to-light ratios of stellar components and reproducing the HI-inferred circular velocity well beyond the limits of the SAMI data. While the method is tailored for fitting integral field kinematic data, it can use other dynamical constraints like central fibre dispersions and \HI circular velocities, and is well-suited for modelling galaxies with a combination of deep imaging and HI and/or optical spectra (resolved or otherwise). Our implementation (MagRite) is computationally efficient and can generate well-resolved models and kinematic maps in under a minute on modern processors.
We report the detection of CO(J=2-1) coincident with the super star cluster (SSC) Mrk 71-A in the nearby Green Pea analog galaxy, NGC 2366. Our NOEMA observations reveal a compact, ~7 pc, molecular cloud whose mass (10^5 M_sun) is similar to that of the SSC, consistent with a high star-formation efficiency, on the order of 0.5. There are two, spatially distinct components separated by 11 km/s. If expanding, these could be due to momentum-driven, stellar wind feedback. Alternatively, we may be seeing the remnant infalling, colliding clouds responsible for triggering the SSC formation. The kinematics are also consistent with a virialized system. These extreme, high-density, star-forming conditions inhibit energy-driven feedback; the co-spatial existence of a massive, molecular cloud with the SSC supports this scenario, and we quantitatively confirm that any wind-driven feedback in Mrk 71-A is momentum-driven, rather than energy-driven. Since Mrk 71-A is a candidate Lyman continuum emitter, this implies that energy-driven superwinds may not be a necessary condition for the escape of ionizing radiation. In addition, the detection of the nebular continuum emission yields an accurate astrometric position for the Mrk 71-A. We also detect four other massive, molecular clouds in this giant star-forming complex.
We live in an age where an enormous amount of astrometric, photometric, asteroseismic, and spectroscopic data of Milky Way stars are being acquired, many orders of magnitude larger than about a decade ago. Thanks to the Gaia astrometric mission and followup ground-based spectroscopic surveys in the next 5-10 years about 10-20 Million stars will have accurate 6D kinematics and chemical composition measurements. KEPLER-2, PLATO, and TESS will provide asteroseismic ages for a good fraction of those. In this article we outline some outstanding problems concerning the formation and evolution of the Milky Way and argue that, due to the complexity of physical processes involved in the formation of disk galaxies, numerical simulations in the cosmological context are needed for the interpretation of Milky Way observations. We also discuss in some detail the formation of the Milky Way thick disk, chemodynamical models, and the effects of radial migration.
We present interferometric and single-dish molecular line observations of the interstellar bullet-outflow source IRAS 05506+2414, whose wide-angle bullet spray is similar to the Orion BN/KL explosive outflow and likely arises from an entirely different mechanism than the classical accretion-disk-driven bipolar flows in young stellar objects. The bullet-outflow source is associated with a large pseudo-disk and three molecular outflows -- a high-velocity outflow (HVO), a medium-velocity outflow (MVO), and a slow, extended outflow (SEO). The size (mass) of the pseudo-disk is 10,350 AU x 6,400 AU (0.64-0.17 Msun); from a model-fit assuming infall and rotation we derive a central stellar mass of 8--19 Msun. The HVO (MVO) has an angular size ~5180 (~3330) AU, and a projected outflow velocity of ~140 km/s (~30 km/s). The SEO size (outflow speed) is ~0.9 pc (~6 km/s). The HVO's axis is aligned with (orthogonal to) that of the SEO (pseudo-disk). The velocity structure of the MVO is unresolved. The scalar momenta in the HVO and SEO are very similar, suggesting that the SEO has resulted from the HVO interacting with ambient cloud material. The bullet spray shares a common axis with the pseudo-disk, and has an age comparable to that of MVO (few hundred years), suggesting that these three structures are intimately linked together. We discuss several models for the outflows in IRAS 05506+2414 (including dynamical decay of a stellar cluster, chance encounter of a runaway star with a dense cloud, and close passage of two protostars), and conclude that 2nd-epoch imaging to derive proper motions of the bullets and nearby stars can help to discriminate between them.
We present abundance measurements of elements O, C, Si and Fe for three gas-rich galaxies at z~5 using observations from the Very Large Telescope (VLT) and the Keck telescope in order to better constrain the early chemical enrichment of gas-rich galaxies. These galaxies show strong Lyman-{\alpha} absorption in the spectra of background quasars, with neutral hydrogen column densities log N${_H{}_I}$(cm$^{-2}$)=20.10$\pm$0.15, 20.10$\pm$0.15, and 20.80$\pm$0.15. Using the undepleted element O, we find the metallicities [O/H] to be in the range of -2.51 to -2.05 dex. Our study has doubled the existing sample of measurements of undepleted elements at z>4.5. Combining our measurements with those from the literature, we find that the N${_H{}_I}$-weighted mean metallicity of z~5 absorbers is consistent with the prediction based on z<4.5 DLAs. Thus, we find no significant evidence of a sudden drop in metallicity at z>4.7 as reported by some prior studies. We also determine the extent of dust depletion using a combination of both the volatile element O and the refractory elements Si and/or Fe. Some of the absorbers show evidence of depletion of elements on dust grains, e.g. low [Si/O] or [Fe/O]. The relative abundances of these absorbers along with other z~5 absorbers from the literature show some peculiarities, e.g. low [C/O] in several absorbers and high [Si/O] in one absorber. Finally, we find that the metallicity vs. velocity dispersion relation of z~5 absorbers may be different from that of lower-redshift absorbers.
We have recently presented strong evidence that chaotic orbits that obey one isolating integral besides energy exist in a toy Hamiltonian model with three degrees of freedom and are bounded by regular orbits that isolate them from the Arnold web. The interval covered by those numerical experiments was equivalent to about one million Hubble times in a galactic context. Here we use a four dimensional map to confirm our previous results and to extend that interval fifty times. We show that, at least within that interval, features found in lower dimension Hamiltonian systems and maps are also present in our study, e.g., within the phase space occupied by a chaotic orbit that obeys one integral there are subspaces where that orbit does not enter and are, instead, occupied by regular orbits that, if tori, bound other chaotic orbits obeying one integral and, if cantori, produce stickiness. We argue that the validity of our results might exceed the time intervals covered by the numerical experiments.
The V380 Ori NE bipolar outflow was imaged in the SiO and CO J = 1 - 0 lines, and dense cores in L1641 were observed in the 2.0-0.89 mm continuum. The highly collimated SiO jet shows point-symmetric oscillation patterns in both position and velocity, which suggests that the jet axis is precessing and the driving source may belong to a non-coplanar binary system. By considering the position and velocity variabilities together, accurate jet parameters were derived. The protostellar system is viewed nearly edge-on, and the jet has a flow speed of 35 km/s and a precession period of 1600 years. The CO outflow length gives a dynamical timescale of 6300 years, and the protostar must be extremely young. The inferred binary separation of 6-70 au implies that this protobinary system may have been formed through the disk instability process. The continuum spectra of L1641 dense cores indicate that the emission comes from dust, and the fits with modified blackbody functions give emissivity power indices of beta = 0.3-2.2. The emissivity index shows a positive correlation with the molecular line width, but no strong correlation with bolometric luminosity or temperature. V380 Ori NE has a particularly low value of beta = 0.3, which tentatively suggests the presence of millimeter-sized dust grains. Because the dust growth takes millions of years, much longer than the protostellar age, this core may have produced large grains in the starless core stage. HH 34 MMS and HH 147 MMS also have low emissivity indices.
Type 1 active galactic nuclei display broad emission lines, regarded as arising from photoionized gas moving in the gravitational potential of a supermassive black hole. The origin of this broad-line region gas is unresolved so far, however. Another component is the dusty torus beyond the broad-line region, likely an assembly of discrete clumps that can hide the region from some viewing angles and make them observationally appear as Type 2 objects. Here we report that these clumps moving within the dust sublimation radius, like the molecular cloud G2 discovered in the Galactic center, will be tidally disrupted by the hole, resulting in some gas becoming bound at smaller radii while other gas is ejected and returns to the torus. The clumps fulfill necessary conditions to be photoionized. Specific dynamical components of tidally disrupted clumps include spiral-in gas as inflow, circularized gas, and ejecta as outflow. We calculate various profiles of emission lines from these clouds, and find they generally agree with H$\beta$ profiles of Palomar-Green quasars. We find that asymmetry, shape and shift of the profiles strongly depend on [O III], luminosity, which we interpret as a proxy of dusty torus angles. Tidally disrupted clumps from the torus may represent the source of the broad-line region gas.
We present accurate resolved $WISE$ photometry of galaxies in the combined SINGS and KINGFISH sample. The luminosities in the W3 12$\mu$m and W4 23$\mu$m bands are calibrated to star formation rates (SFRs) derived using the total infrared luminosity, avoiding UV/optical uncertainties due to dust extinction corrections. The W3 relation has a 1-$\sigma$ scatter of 0.15 dex over nearly 5 orders of magnitude in SFR and 12$\mu$m luminosity, and a range in host stellar mass from dwarf (10$^7$ M$_\odot$) to $\sim3\times$M$_\star$ (10$^{11.5}$ M$_\odot$) galaxies. In the absence of deep silicate absorption features and powerful active galactic nuclei, we expect this to be a reliable SFR indicator chiefly due to the broad nature of the W3 band. By contrast the W4 SFR relation shows more scatter (1-$\sigma =$ 0.18 dex). Both relations show reasonable agreement with radio continuum-derived SFRs and excellent accordance with so-called "hybrid" H$\alpha + 24 \mu$m and FUV$+$24$\mu$m indicators. Moreover, the $WISE$ SFR relations appear to be insensitive to the metallicity range in the sample. We also compare our results with IRAS-selected luminous infrared galaxies, showing that the $WISE$ relations maintain concordance, but systematically deviate for the most extreme galaxies. Given the all-sky coverage of $WISE$ and the performance of the W3 band as a SFR indicator, the $L_{12\mu \rm m}$ SFR relation could be of great use to studies of nearby galaxies and forthcoming large area surveys at optical and radio wavelengths.
We present a multi-component structural analysis of the internal structure of $1074$ high redshift massive galaxies at $1<z<3$ from the CANDELS HST Survey. In particular we examine galaxies best-fit by two structural components, and thus likely forming discs and bulges. We examine the stellar mass, star formation rates, and colours of both the inner `bulge' and outer `disc' components for these systems using SED information from the resolved ACS+WFC3 HST imaging. We find that the majority of both inner and outer components lie in the star-forming region of UVJ space ($68$ and $90$ per cent respectively). However, the inner portions, or the likely forming bulges, are dominated by dusty star formation. Furthermore, we show that the outer components of these systems have a higher star formation rate than their inner regions, and the ratio of star formation rate between `disc' and `bulge' increases at lower redshifts. Despite the higher star formation rate of the outer component, the stellar mass ratio of inner to outer component remains constant through this epoch. This suggests that there is mass transfer from the outer to inner components for typical two component forming systems, thus building bulges from disks. Finally, using Chandra data we find that the presence of an AGN is more common in both $1$-component spheroid-like galaxies and $2$-component systems ($13\pm3$ and $11\pm2$ per cent) than in $1$-component disc-like galaxies ($3\pm1$ per cent), demonstrating that the formation of a central inner-component likely triggers the formation of central massive black holes in these galaxies.
Multiwavelength deep observations are a key tool to understand the origin of the diffuse light in clusters of galaxies: the intra-cluster light (ICL). For this reason, we take advantage of the Hubble Frontier Fields survey to investigate the properties of the stellar populations of the ICL of its 6 massive intermediate redshift (0.3<z<0.6) clusters. We carry on this analysis down to a radial distance of ~120 kpc from the brightest cluster galaxy. We found that the average metallicity of the ICL is [Fe/H] ~-0.5, compatible with the value of the outskirts of the Milky Way. The mean stellar ages of the ICL are between 2 to 6 Gyr younger than the most massive galaxies of the clusters. Those results suggest that the ICL of these massive (> 10^15 Msol) clusters is formed by the stripping of MW-like objects that have been accreted at z<1, in agreement with current simulations. We do not find any significant increase in the fraction of light of the ICL with cosmic time, although the redshift range explored is narrow to derive any strong conclusion. When exploring the slope of the stellar mass density profile, we found that the ICL of the HFF clusters follows the shape of their underlying dark matter haloes, in agreement with the idea that the ICL is the result of the stripping of galaxies at recent times.
Contributed paper to the Conference "Francesco's Legacy: Star Formation in Space and Time", in memory of Francesco Palla (1954-2016), held in Florence, June 5-9, 2017
During the start of a survey program using FORS2 long slit spectroscopy on planetary nebulae (PN) and their haloes, we serendipitously discovered six background emission line galaxies (ELG) with redshifts of z = 0.2057, 0.3137, 0.37281, 0.4939, 0.7424 and 0.8668. Thus they clearly do not belong to a common cluster structure. We derived the major physical properties of the targets. Since the used long slit covers a sky area of only 570 arcsec^2, we discuss further potential of serendipitous discoveries in archival data, beside the deep systematic work of the ongoing and upcoming big surveys. We conclude that archival data provide a decent potential for extending the overall data on ELGs without any selection bias.
HARPS-N spectra with S/N > 250 and MARCS model atmospheres were used to derive abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, and Y in ten stars from the Kepler LEGACY sample (including the binary pair 16 Cyg A and B) selected to have metallicities in the range -0.15 < [Fe/H] < +0.15 and ages between 1 and 7 Gyr. Stellar gravities were obtained from seismic data and effective temperatures were determined by comparing non-LTE iron abundances derived from FeI and FeII lines. Available non-LTE corrections were also applied when deriving abundances of the other elements. The results support the [X/Fe]-age relations previously found for solar twins. [Mg/Fe], [Al/Fe], and [Zn/Fe] decrease by ~0.1 dex over the lifetime of the Galactic thin disk due to delayed contribution of iron from Type Ia supernovae relative to prompt production of Mg, Al, and Zn in Type II supernovae. [Y/Mg] and [Y/Al], on the other hand, increase by ~0.3 dex, which can be explained by an increasing contribution of s-process elements from low-mass AGB stars as time goes on. The trends of [C/Fe] and [O/Fe] are more complicated due to variations of the ratio between refractory and volatile elements among stars of similar age. Two stars with about the same age as the Sun show very different trends of [X/H] as a function of elemental condensation temperature Tc and for 16 Cyg, the two components have an abundance difference, which increases with Tc. These anomalies may be connected to planet-star interactions.
We present the UV photometry of the globular cluster NGC 1851 using images acquired with the Ultra-violet Imaging Telescope (UVIT) onboard the ASTROSAT satellite. PSF-fitting photometric data derived from images in two far-UV (FUV) filters and one near-UV (NUV) filter are used to construct color-magnitude diagrams (CMD), in combination with HST and ground-based optical photometry. In the FUV, we detect only the bluest part of the cluster horizontal branch (HB); in the NUV, we detect the full extent of the HB, including the red HB, blue HB and a small number of RR Lyrae stars. UV variability was detected in 18 RR Lyrae stars, and 3 new variables were also detected in the central region. The UV/optical CMDs are then compared with isochrones of different age and metallicity (generated using Padova and BaSTI models) and synthetic HB (using helium enhanced $Y^2$ models). We are able to identify two populations among the HB stars, which are found to have either an age range of 10-12~Gyr, or a range in Y$_{ini}$ of 0.23 - 0.28, for a metallicity of [Fe/H] =$-$1.2 to $-$1.3. These estimations from the UV CMDs are consistent with those from optical studies. The almost complete sample of the HB stars tend to show a marginal difference in spatial/azimuthal distribution among the blue and red HB stars. This study thus show cases the capability of UVIT, with its excellent resolution and large field of view, to study the hot stellar population in Galactic globular clusters.
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We study the presence of tidal features associated with ultra diffuse galaxies (UDGs) in galaxy clusters. Specifically, we stack deep Subaru images of UDGs in the Coma cluster to determine whether they show position angle twists at large radii. Selecting galaxies with central surface brightness (g-band) >24 magarcsec^{-2} and projected half-light radius >1.5 kpc, we identify 287 UDGs in the Yagi et al. 2016 catalog of low surface brightness Coma objects. The UDGs have apparent spheroidal shapes with median Sersic index ~ 0.8 and median axis-ratio ~ 0.7. The images are processed by masking all background objects and rotating to align the major axis before stacking them in bins of properties such as axis ratio, angle of major axis with respect to the cluster center and separation from cluster center. Our image stacks reach further than 7 kpc (~4r_e). Analysis of the isophotes of the stacks reveal that the ellipticity remains constant up to the last measured point, which means that the individual galaxies have a non-varying position angle and axis ratio and show no evidence for tidal disruption out to ~ 4r_e. We demonstrate this explicitly by comparing our stacks with stacks of model UDGs with and without tidal features in their outskirts. We infer that the average tidal radius of the Coma UDGs is >7 kpc and estimate that the average dark matter fraction within the tidal radius of the UDGs inhabiting the innermost 0.5 Mpc of Coma is > 99%.
In recent years, due to the acquisition of higher-quality data covering greater survey volumes, streaming motions observed in the Galactic disc have gained importance in understanding the processes involved in galaxy formation and evolution. Here, we use data from the Radial Velocity Experiment (RAVE) and the Tycho-Gaia astrometric solution catalogue (TGAS) to compute the velocity fields yielded by the radial (VR), azimuthal (Vphi) and vertical (Vz) components of associated Galactocentric velocity. We search in particular for variation in all three velocity components with distance above and below the disc midplane, as well as how each component of Vz (line-of-sight and tangential velocity projections) modifies the obtained vertical structure. To study the dependence of velocity on proper motion and distance we use two main samples: a RAVE sample including proper motions from the Tycho-2, PPMXL and UCAC4 catalogues, and a RAVE-TGAS sample with inferred distances and proper motions from the TGAS and UCAC5 catalogues. In both samples, we identify asymmetries in VR and Vz. Below the plane we find the largest radial gradient to be dVR / dR = -7.01+- 0.61 km\s kpc, in agreement with recent studies. Above the plane we find a similar gradient with dVR / dR= -9.42+- 1.77 km\s kpc. By comparing our results with previous studies, we find that the structure in Vz is strongly dependent on the adopted proper motions. Using the Galaxia Milky Way model, we demonstrate that distance uncertainties can create artificial wave-like patterns. In contrast to previous suggestions of a breathing mode seen in RAVE data, our results support a combination of bending and breathing modes, likely generated by a combination of external or internal and external mechanisms. This can be interpreted as a superposition of more than one wave existing simultaneously in the Milky Way disc.
We analyse the properties of circumgalactic gas around simulated galaxies in the redshift range z >= 3, utilising a new sample of cosmological zoom simulations. These simulations are intended to be representative of the observed samples of Lyman-alpha emitters recently obtained with the MUSE instrument (halo masses ~10^10-10^11 solar masses). We show that supernova feedback has a significant impact on both the inflowing and outflowing circumgalactic medium by driving outflows, reducing diffuse inflow rates, and by increasing the neutral fraction of inflowing gas. By temporally stacking simulation outputs we find that significant net mass exchange occurs between inflowing and outflowing phases: none of the phases are mass-conserving. In particular, we find that the mass in neutral outflowing hydrogen declines exponentially with radius as gas flows outwards from the halo centre. This is likely caused by a combination of both fountain-like cycling processes and gradual photo/collisional ionization of outflowing gas. Our simulations do not predict the presence of fast-moving neutral outflows in the CGM. Neutral outflows instead move with modest radial velocities (~ 50 kms^-1), and the majority of the kinetic energy is associated with tangential rather than radial motion.
We have conducted a two-layered spectroscopic survey (1'x1' ultra deep and 3'x3' deep regions) in the Hubble Ultra Deep Field (HUDF) with the Multi Unit Spectroscopic Explorer (MUSE). The combination of a large field of view, high sensitivity, and wide wavelength coverage provides an order of magnitude improvement in spectroscopically confirmed redshifts in the HUDF; i.e., 1206 secure spectroscopic redshifts for HST continuum selected objects, which corresponds to 15% of the total (7904). The redshift distribution extends well beyond z>3 and to HST/F775W magnitudes as faint as ~30 mag (AB, 1-sigma). In addition, 132 secure redshifts were obtained for sources with no HST counterparts that were discovered in the MUSE data cubes by a blind search for emission-line features. In total, we present 1338 high quality redshifts, which is a factor of eight increase compared with the previously known spectroscopic redshifts in the same field. We assessed redshifts mainly with the spectral features [OII] at z<1.5 (473 objects) and Lya at 2.9<z<6.7 (692 objects). With respect to F775W magnitude, a 50% completeness is reached at 26.5 mag for ultra deep and 25.5 mag for deep fields, and the completeness remains >~20% up to 28-29 mag and ~27 mag, respectively. We used the determined redshifts to test continuum color selection (dropout) diagrams of high-z galaxies. The selection condition for F336W dropouts successfully captures ~80% of the targeted z~2.7 galaxies. However, for higher redshift selections (F435W, F606W, and F775W dropouts), the success rates decrease to ~20-40%. We empirically redefine the selection boundaries to make an attempt to improve them to ~60%. The revised boundaries allow bluer colors that capture Lya emitters with high Lya equivalent widths falling in the broadbands used for the color-color selection. Along with this paper, we release the redshift and line flux catalog.
The Galactic halo has a complex assembly history, which can be seen in its wealth of kinematic and chemical substructure. Globular clusters lose stars through tidal interactions with the Galaxy and cluster evaporation processes, meaning that they are inevitably a source of halo stars. These "migrants" from globular clusters can be recognized in the halo field by the characteristic light element abundance anticorrelations that are commonly observed only in globular cluster stars, and the number of halo stars that can be chemically tagged to globular clusters can be used to place limits on the formation pathways of those clusters.
We present optical and near-infrared stellar polarization observations toward the dark filamentary clouds associated with IC5146. The data allow us to investigate the dust properties (this paper) and the magnetic field structure (Paper II). A total of 2022 background stars were detected in $R_{c}$-, $i'$-, $H$-, and/or $K$-bands to $A_V \lesssim 25$ mag. The ratio of the polarization percentage at different wavelengths provides an estimate of $\lambda_{max}$, the wavelength of peak polarization, which is an indicator of the small-size cutoff of the grain size distribution. The grain size distribution seems to significantly change at $A_V \sim$ 3 mag, where both the average and dispersion of $P_{R_c}/P_{H}$ decrease. In addition, we found $\lambda_{max}$ $\sim$ 0.6-0.9 $\mu$m for $A_V>2.5$ mag, which is larger than the $\sim$ 0.55 $\mu$m in the general ISM, suggesting that grain growth has already started in low $A_V$ regions. Our data also reveal that polarization efficiency (PE $\equiv P_{\lambda}/A_V$) decreases with $A_V$ as a power-law in $R_c$-, $i'$-, and $K$-bands with indices of -0.71$\pm$0.10, -1.23$\pm$0.10 and -0.53$\pm$0.09. However, $H$-band data show a power index change; the PE varies with $A_V$ steeply (index of -0.95$\pm$0.30) when $A_V < 2.88\pm0.67$ mag but softly (index of -0.25$\pm$0.06) for greater $A_V$ values. The soft decay of PE in high $A_V$ regions is consistent with the Radiative Aligned Torque model, suggesting that our data trace the magnetic field to $A_V \sim 20$ mag. Furthermore, the breakpoint found in $H$-band is similar to the $A_V$ where we found the $P_{R_c}/P_{H}$ dispersion significantly decreased. Therefore, the flat PE-$A_V$ in high $A_V$ regions implies that the power index changes result from additional grain growth.
We investigate roles of magnetic activity in the Galactic bulge region in driving large-scale outflows of size ~ 10 kpc. Magnetic buoyancy and breakups of channel flows formed by magnetorotational instability excite Poynting flux by the magnetic tension force. A three-dimensional global numerical simulation shows that the average luminosity of such Alfvenic Poynting flux is 10^{40} - 10^{41} erg s^{-1}. We examine the energy and momentum transfer from the Poynting flux to the gas by solving time-dependent hydrodynamical simulations with explicitly taking into account low-frequency Alfvenic waves of period of 0.5 Myr in a one-dimensional vertical magnetic flux tube. The Alfvenic waves propagate upward into the Galactic halo, and they are damped through the propagation along meandering magnetic field lines. If the turbulence is nearly trans-Alfvenic, the wave damping is significant, which leads to the formation of an upward propagating shock wave. At the shock front, the temperature >~ 5 x 10^6 K, the density ~ 1 cm^{-3}, and the outflow velocity ~ 400-500 km/s at a height ~10 kpc, which reasonably explain the basic physical properties of the thermal component of the Fermi bubbles.
It is widely believed that the cool gas clouds traced by MgII absorption, within a velocity offset of 5000 km/s relative to the background quasar are mostly associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening absorber systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. (2011, hereinafter BBM) has seriously questioned this paradigm, by showing that the number density of intervening MgII absorbers towards the 45 blazars in their sample is nearly 2 times the expectation based on the MgII absorption systems seen towards normal QSOs. Given its serious implications, it becomes important to revisit this finding, by enlarging the blazar sample and subjecting it to an independent analysis. Here, we first report the outcome of our re-analysis of the available spectroscopic data for the BBM sample itself. Our analysis of the BBM sample reproduces their claimed factor of 2 excess of dN/dz along blazar sightlines, vis-a-vis normal QSOs. We have also assembled a ~3 times larger sample of blazars, albeit with moderately sensitive optical spectra. Using this sample together with the BBM sample, our analysis shows that the dN/dz of the MgII absorbers statistically matches that known for normal QSO sightlines. Further, the analysis indicates that associated absorbers might be contributing significantly to the estimated dN/dz upto offset speeds \Delta v ~0.2c relative to the blazar.
The composition and morphology of the interstellar medium in starburst galaxies has been well investigated, but the magnetic field properties are still uncertain. The nearby starburst galaxy M82 provides a unique opportunity to investigate the mechanisms leading to the amplification and reduction of turbulent and regular magnetic fields. Possible scenarios of the contribution of the magnetic field to the star-formation rate are evaluated. Archival data from the VLA and WSRT were combined and re-reduced to cover the wavelength regime between 3cm and 22cm. All observations revealed polarised emission in the inner part of the galaxy, while extended polarised emission up to a distance of 2kpc from the disk was only detected at 18cm and 22cm. The observations hint at a magnetised bar in the inner part of the galaxy. We calculate the mass inflow rate due to magnetic stress of the bar to 7.1 solar masses per year, which can be a significant contribution to the star-formation rate of M82 of approximately 13 solar masses per year. The halo shows polarised emission, which might be the remnant of a regular disk field. Indications for a helical field in the inner part of the outflow cone are provided. The coherence length of the magnetic field in the centre is similar to the size of giant molecular clouds. Using polarisation spectra more evidence for a close coupling of the ionised gas and the magnetic field as well as a two-phase magnetic field topology were found. Electron densities in the halo are similar to the ones found in the Milky Way. The magnetic field morphology is similar to the one in other nearby starburst galaxies with possible large-scale magnetic loops in the halo and a helical magnetic field inside the outflow cones. The special combination of a magnetic bar and a circumnuclear ring are able to significantly raise the star-formation rate in this galaxy by magnetic braking.
We studied the spatial distribution of young and old stellar populations along the western half part of the minor axis of the Large Magellanic Cloud (LMC) using Washington MT1 photometry of selected fields, which span a deprojected distance range from the LMC bar centre out to ~ 31.6 kpc. We found that both stellar populations share a mean LMC limiting radius of 8.9+-0.4 kpc; old populations are three times more dense that young populations at that LMC limit. When comparing this result with recent values for the LMC extension due to north, the old populations resulted significantly more elongated than the young ones. Bearing in mind previous claims that the elongation of the outermost LMC regions may be due to the tidal effects of the Milky Way (MW), our findings suggest that such a tidal interaction should not have taken place recently. The existence of young populations in the outermost western regions also supports previous results about ram pressure stripping effects of the LMC gaseous disc due to the motion of the LMC in the MW halo.
In a complete sample of local 14-195 keV selected AGNs and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, 8 AGNs and 5 inactive galaxies. The stellar velocity fields show a disk-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disk structure, and which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies.
This paper is a follow-up of a previous paper about the M82 galaxy and its halo based on Planck observations. As in the case of M82, so also for the M81 galaxy a substantial North-South and East-West temperature asymmetry is found, extending up to galactocentric distances of about $1.5^\circ$. The temperature asymmetry is almost frequency independent and can be interpreted as a Doppler-induced effect related to the M81 halo rotation and/or triggered by the gravitational interaction of the galaxies within the M81 Group. Along with the analogous study of several nearby edge-on spiral galaxies, the CMB temperature asymmetry method thus is shown to act as a direct tool to map the galactic haloes and/or the intergalactic bridges, invisible in other bands or by other methods.
Investigating variability at the earliest stages of low-mass star formation is fundamental in understanding how a protostar assembles mass. While many simulations of protostellar disks predict non-steady accretion onto protostars, deeper investigation requires robust observational constraints on the frequency and amplitude of variability events characterised across the observable SED. In this study, we develop methods to robustly analyse repeated observations of an area of the sky for submillimetre variability in order to determine constraints on the magnitude and frequency of deeply embedded protostars. We compare \mbox{850 $\mu$m} JCMT Transient Survey data with archival JCMT Gould Belt Survey data to investigate variability over 2-4 year timescales. Out of 175 bright, independent emission sources identified in the overlapping fields, we find 7 variable candidates, 5 of which we classify as \textit{Strong} and the remaining 2 as \textit{Extended} to indicate the latter are associated with larger-scale structure. For the \textit{Strong} variable candidates, we find an average fractional peak brightness change per year of |4.0|\% yr$^{-1}$ with a standard deviation of $2.7\%\mathrm{\:yr}^{-1}$. In total, 7\% of the protostars associated with \mbox{850 $\mu$m} emission in our sample show signs of variability. Four of the five \textit{Strong} sources are associated with a known protostar. The remaining source is a good follow-up target for an object that is anticipated to contain an enshrouded, deeply embedded protostar. In addition, we estimate the \mbox{850 $\mu$m} periodicity of the submillimetre variable source, EC 53, to be \mbox{567 $\pm$ 32 days} based on the archival Gould Belt Survey data.
The dynamics of the high-velocity compact molecular cloud CO-0.40-0.22 have been interpreted as evidence for a $\sim10^{5}M_{\odot}$ black hole within 60 pc of Sgr A*. Recently, Oka et al. have identified a compact millimetre-continuum source, CO-0.40-0.22*, with this candidate black hole. Here we present a collation of radio and infrared data at this location. ATCA constraints on the radio spectrum, and the detection of a mid-infrared counterpart, are in tension with an Sgr A*-like model for CO-0.40-0.22* despite the comparable bolometric to Eddington luminosity ratios under the IMBH interpretation. A protostellar-disk scenario is, however, tenable. CO-0.40-0.22(*) is associated with an arrowhead-shaped infrared-dark cloud (which we call the Freccia Rossa). Radio-continuum observations reveal a candidate HII region associated with the system. If the $V_{\rm LSR}\approx70$ km s$^{-1}$ systemic velocity of CO-0.40-0.22 is common to the entire Freccia Rossa system, we hypothesise that it is the remnant of a high-velocity cloud that has plunged into the Milky Way from the Galactic halo.
Mean field electrodynamics (MFE) facilitates practical modeling of secular, large scale properties of magnetohydrodynamic or plasma systems with fluctuations. Practitioners commonly assume wide scale separation between mean and fluctuating quantities, to justify equality of ensemble and spatial or temporal averages. Often however, real systems do not exhibit such scale separation. This raises two questions: (1) what are the appropriate generalized equations of MFE in the presence of mesoscale fluctuations? (2) how precise are theoretical predictions from MFE? We address both by first deriving the equations of MFE for different types of averaging, along with mesoscale correction terms that depend on the ratio of averaging scale to variation scale of the mean. We then show that even if these terms are small, predictions of MFE can still have a significant precision error. This error has an intrinsic contribution from the dynamo input parameters and a contribution from the difference in the way observations and theory are projected through the measurement kernel. Minimizing the sum of these contributions can identify an optimal scale of averaging that makes the theory maximally precise. The precision error is important to quantify when comparing to observations because it quantifies the resolution of predictive power. We exemplify these principles for galactic dynamos, comment on broader implications, and identify possibilities for further work.
Although the final observations of the Spitzer Warm Mission are currently scheduled for March 2019, it can continue operations through the end of the decade with no loss of photometric precision. As we will show, there is a strong science case for extending the current Warm Mission to December 2020. Spitzer has already made major impacts in the fields of exoplanets (including microlensing events), characterizing near Earth objects, enhancing our knowledge of nearby stars and brown dwarfs, understanding the properties and structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to study galaxy birth and evolution. By extending Spitzer through 2020, it can continue to make ground-breaking discoveries in those fields, and provide crucial support to the NASA flagship missions JWST and WFIRST, as well as the upcoming TESS mission, and it will complement ground-based observations by LSST and the new large telescopes of the next decade. This scientific program addresses NASA's Science Mission Directive's objectives in astrophysics, which include discovering how the universe works, exploring how it began and evolved, and searching for life on planets around other stars.
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Local Group (LG) galaxies have relatively accurate SFHs and metallicity evolution derived from resolved CMD modeling, and thus offer a unique opportunity to explore the efficacy of estimating stellar mass M$_{\star}$ of real galaxies based on integrated stellar luminosities. Building on the SFHs and metallicity evolution of 40 LG dwarf galaxies, we carried out a comprehensive study of the influence of SFHs, metallicity evolution and dust extinction on the UV-to-NIR color-$\mathcal{M/L}$ (color-log$\Upsilon_{\star}$($\lambda$)) relations and M$_{\star}$ estimation of local universe galaxies. We find that: The LG galaxies follow color-log$\Upsilon_{\star}$($\lambda$) relations that fall in between the ones calibrated by previous studies; Optical color-log$\Upsilon_{\star}$($\lambda$) relations at higher metallicities ([M/H]) are generally broader and steeper; The SFH "concentration" does not significantly affect the color-log$\Upsilon_{\star}$($\lambda$) relations; Light-weighted ages and [M/H] together constrain log$\Upsilon_{\star}$($\lambda$) with uncertainties ranging from $\lesssim$ 0.1 dex for the NIR up to 0.2 dex for the optical passbands; Metallicity evolution induces significant uncertainties to the optical but not NIR $\Upsilon_{\star}$($\lambda$) at given light-weighted ages and [M/H]; The $V$ band is the ideal luminance passband for estimating $\Upsilon_{\star}$($\lambda$) from single colors, because the combinations of $\Upsilon_{\star}$($V$) and optical colors such as $B-V$ and $g-r$ exhibit the weakest systematic dependence on SFHs, [M/H] and dust extinction; Without any prior assumption on SFHs, M$_{\star}$ is constrained with biases $\lesssim$ 0.3 dex by the optical-to-NIR SED fitting. Optical passbands alone constrain M$_{\star}$ with biases $\lesssim$ 0.4 dex (or $\lesssim$ 0.6 dex) when dust extinction is fixed (or variable) in SED fitting. [abridged]
Observational and theoretical arguments increasingly suggest that the initial mass function (IMF) of stars may depend systematically on environment, yet most galaxy formation models to date assume a universal IMF. Here we investigate simulations of the formation of Milky Way analogues run with an empirically derived metallicity-dependent IMF and the moving-mesh code AREPO in order to characterize the associated uncertainties. In particular, we compare a constant Chabrier and a varying metallicity-dependent IMF in cosmological, magneto-hydrodynamical zoom-in simulations of Milky Way-sized halos. We find that the non-linear effects due to IMF variations typically have a limited impact on the morphology and the star formation histories of the formed galaxies. Our results support the view that constraints on stellar-to-halo mass ratios, feedback strength, metallicity evolution and metallicity distributions are in part degenerate with the effects of a non-universal, metallicity-dependent IMF. Interestingly, the empirical relation we use between metallicity and the high mass slope of the IMF does not aid in the quenching process. It actually produces up to a factor of 2-3 more stellar mass if feedback is kept constant. Additionally, the enrichment history and the z = 0 metallicity distribution are significantly affected. In particular, the alpha enhancement pattern shows a steeper dependence on iron abundance in the metallicity-dependent model, in better agreement with observational constraints.
There is considerable interest in understanding the demographics of galaxies within the local universe (defined, for our purposes, as the volume within a radius of 200 Mpc or z<0.05). In this pilot paper we investigate the redshift completeness of catalogs of such nearby galaxies. Our sample consists of host galaxies of nearby, z_SN < 0.05, supernovae (SNe) discovered by the flux-limited ASAS-SN survey. Thanks to their brilliance SNe are easy to find and with some care can be used to study galaxy populations. In particular, type Ia SNe arise in both old and young stellar populations and thus can be used to study the general demographics of galaxies. We define the redshift completeness fraction (RCF) as the number of SN host galaxies with known redshift prior to SN discovery, determined, in this case, via the NASA Extragalactic Database (NED), divided by the total number of newly discovered SNe. By raw numbers, we find RCF ~ 0.8 for z < 0.03. We examine the distribution of hosts with and without cataloged redshifts as a function of absolute magnitude and redshift, and, unsurprisingly, find that higher-$z$ and fainter hosts are less likely to have a known redshift prior to the detection of the SN. We conclude with thoughts on the future improvement of RCF measurements, which will benefit greatly from upcoming surveys.
Using new APEX and JCMT spectroscopy of the CO 2-1 line, we undertake a controlled study of cold molecular gas in moderately luminous Active Galactic Nuclei (AGN) and inactive galaxies from the Luminous Local AGN with Matched Analogs (LLAMA) survey. We use spatially resolved infrared photometry of the LLAMA galaxies from 2MASS, WISE, IRAS & Herschel, corrected for nuclear emission using multi-component spectral energy distribution (SED) fits, to examine the dust-reprocessed star-formation rates (SFRs), molecular gas fractions and star formation efficiencies (SFEs) over their central 1 - 3 kpc. We find that the gas fractions and central SFEs of both active and inactive galaxies are similar when controlling for host stellar mass and morphology (Hubble type). The equivalent central molecular gas depletion times are consistent with the discs of normal spiral galaxies in the local Universe. Despite energetic arguments that the AGN in LLAMA should be capable of disrupting the observable cold molecular gas in their central environments, our results indicate that nuclear radiation only couples weakly with this phase. We find a mild preference for obscured AGN to contain higher amounts of central molecular gas, which suggests a connection between AGN obscuration and the gaseous environment of the nucleus. Systems with depressed SFEs are not found among the LLAMA AGN. We speculate that the processes that sustain the collapse of molecular gas into dense pre-stellar cores may also be a prerequisite for the inflow of material on to AGN accretion disks.
We investigate the relationship between the black hole accretion rate (BHAR) and star-formation rate (SFR) for Milky Way (MW) and Andromeda (M31)-mass progenitors from z = 0.2 - 2.5. We source galaxies from the Ks-band selected ZFOURGE survey, which includes multi-wavelenth data spanning 0.3 - 160um. We use decomposition software to split the observed SEDs of our galaxies into their active galactic nuclei (AGN) and star-forming components, which allows us to estimate BHARs and SFRs from the infrared (IR). We perform tests to check the robustness of these estimates, including a comparison to BHARs and SFRs derived from X-ray stacking and far-IR analysis, respectively. We find as the progenit- ors evolve, their relative black hole-galaxy growth (i.e. their BHAR/SFR ratio) increases from low to high redshift. The MW-mass progenitors exhibit a log-log slope of 0.64 +/- 0.11, while the M31-mass progenitors are 0.39 +/- 0.08. This result contrasts with previous studies that find an almost flat slope when adopting X-ray/AGN-selected or mass-limited samples and is likely due to their use of a broad mixture of galaxies with different evolutionary histories. Our use of progenitor-matched samples highlights the potential importance of carefully selecting progenitors when searching for evolutionary relationships between BHAR/SFRs. Additionally, our finding that BHAR/SFR ratios do not track the rate at which progenitors quench casts doubts over the idea that the suppression of star-formation is predominantly driven by luminous AGN feedback (i.e. high BHARs).
We report direct evidence of pre-processing of the galaxies residing in galaxy groups falling into galaxy clusters drawn from the Local Cluster Substructure Survey (LoCuSS). 34 groups have been identified via their X-ray emission in the infall regions of 23 massive ($\rm \langle M_{200}\rangle = 10^{15}\,M_{\odot}$) clusters at $0.15<z<0.3$. Highly complete spectroscopic coverage combined with 24 $\rm\mu$m imaging from Spitzer allows us to make a consistent and robust selection of cluster and group members including star forming galaxies down to a stellar mass limit of $\rm M_{\star} = 2\times10^{10}\,M_{\odot}$. The fraction $\rm f_{SF}$ of star forming galaxies in infalling groups is lower and with a flatter trend with respect to clustercentric radius when compared to the rest of the cluster galaxy population. At $\rm R\approx1.3\,r_{200}$ the fraction of star forming galaxies in infalling groups is half that in the cluster galaxy population. This is direct evidence that star formation quenching is effective in galaxies already prior to them settling in the cluster potential, and that groups are favourable locations for this process.
We present results from deep (380 ks) \textit{Chandra} observations of the AGN outburst in the massive early-type galaxy NGC 4472. We detect cavities in the gas coincident with the radio lobes and estimate the eastern and western lobe enthalpy to be $(1.1 \pm 0.5 )\times 10^{56}$ erg and $(3 \pm 1 )\times 10^{56}$ erg, and the average power required to inflate the lobes to be $(1.8 \pm 0.9)\times 10^{41}$ erg s$^{-1}$ and $(6 \pm 3)\times 10^{41}$ erg s$^{-1}$, respectively. We also detect enhanced X-ray rims around the radio lobes with sharp surface brightness discontinuities between the shells and the ambient gas. The temperature of the gas in the shells is less than that of the ambient medium, suggesting that they are not AGN-driven shocks but rather gas uplifted from the core by the buoyant rise of the radio bubbles. We estimate the energy required to lift the gas to be up to $(1.1 \pm 0.3 )\times 10^{56}$ erg and $(3 \pm 1 )\times 10^{56}$ erg for the eastern and western rim respectively, constituting a significant fraction of the total outburst energy. A more conservative estimate suggests that the gas in the rim was uplifted a smaller distance, requiring only $20-25\%$ of this energy. In either case, if a significant fraction of this uplift energy is thermalized via hydrodynamic instabilities or thermal conduction, our results suggest that it could be an important source of heating in cool core clusters and groups. We also find evidence for a central abundance drop in NGC 4472. The iron abundance profile shows that the region along the cavity system has a lower metallicity than the surrounding, undisturbed gas, similar to the central region. This also shows that bubbles have lifted low-metallicity gas from the center.
We use a semi-empirical model to reproduce the 0.1-10um spectral energy distribution (SED) of a sample of 85 luminous quasars. In the model, the continuum emission from the accretion disk as well as the nebular lines are represented by a single empirical template (disk), where differences in the optical spectral index are reproduced by varying the amount of extinction. The near- and mid-infrared emission of the AGN-heated dust is modelled as the combination of two black-bodies (dust). The model fitting shows that the disk and dust components are remarkably uniform among individual quasars, with differences in the observed SED largely accounted for by varying levels of obscuration in the disk as well as differences in the relative luminosity of the disk and dust components. By combining the disk-subtracted SEDs of the 85 quasars, we generate a template for the 1-10um emission of the AGN-heated dust. Additionally, we use a sample of local Seyfert 1 galaxies with full spectroscopic coverage in the 0.37um to 39um range to demonstrate a method for stitching together spectral segments obtained with different PSF and extraction apertures. We show that the disk and dust templates obtained from luminous quasars also reproduce the optical-to-mid-infrared spectra of local Seyfert 1s when the contribution from the host galaxy is properly subtracted.
Since its launch in 1999, the Chandra X-ray observatory has discovered several dozen X-ray jets associated with powerful quasars. In many cases the X-ray spectrum is hard and appears to come from a second spectral component. The most popular explanation for the kpc-scale X-ray emission in these cases has been inverse-Compton (IC) scattering of Cosmic Microwave Background (CMB) photons by relativistic electrons in the jet (the IC/CMB model). Requiring the IC/CMB emission to reproduce the observed X-ray flux density inevitably predicts a high level of gamma-ray emission which should be detectable with the Fermi Large Area Telescope (LAT). In previous work, we found that gamma-ray upper limits from the large scale jets of 3C 273 and PKS 0637-752 violate the predictions of the IC/CMB model. Here we present Fermi/LAT flux density upper limits for the X-ray jets of four additional sources: PKS 1136-135, PKS 1229-021, PKS 1354+195, and PKS 2209+080, and show that these limits violate the IC/CMB predictions at a very high significance level. We also present new Hubble Space Telescope (HST) observations of the quasar PKS 2209+080 showing a newly detected optical jet, and Atacama Large Millimeter/submillimeter Array (ALMA) band 3 and 6 observations of all four sources, which provide key constraints on the spectral shape that enable us to rule out the IC/CMB model.
The escape of ultraviolet photons from the densest regions of the interstellar medium (ISM) --- Giant Molecular Clouds (GMCs) --- is a poorly constrained parameter which is vital to understanding the ionization of the ISM and the intergalactic medium. We characterize the escape fraction, f$_{\text{esc,GMC}}$, from a suite of individual GMC simulations with masses in the range 10$^{4-6}$ M$_{\odot}$ using the adaptive-mesh refinement code FLASH. We find significantly different f$_{\text{esc,GMC}}$ depending on the GMC mass which can reach $>$90\% in the evolution of 5$\times$10$^4$ and 10$^{5}$ M$_{\odot}$ clouds or remain low at $\sim$5\% for most of the lifetime of more massive GMCs. All clouds show fluctuations over short, sub-Myr timescales produced by flickering HII regions. We combine our results to calculate the total escape fraction (f$_{\text{esc,tot}}$) from GMC populations in dwarf starburst and spiral galaxies by randomly drawing clouds from a GMC mass distribution (dN/dM$\propto$M$^{\alpha}$, where $\alpha$ is either -1.5 or -2.5) over fixed time intervals. We find typical f$_{\text{esc,tot}}$ values of 8\% for both the dwarf and spiral models. The fluctuations of f$_{\text{esc,tot}}$, however, are much larger for the dwarf models with values as high as 90\%. The photons escaping from the 5$\times$10$^4$ and 10$^{5}$ M$_{\odot}$ GMCs are the dominant contributors to f$_{\text{esc,tot}}$ in all cases. We also show that the accompanying star formation rates (SFRs) of our model ($\sim$2$\times$10$^{-2}$ and 0.73 M$_{\odot}$yr$^{-1}$) are consistent with observations of SFRs in dwarf starburst and spiral galaxies, respectively.
We present a spectroscopic redshift catalog from the LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap (SGC), which is designed to observe all sources (Galactic and extra-galactic) by using repeating observations with a limiting magnitude of $r=18.1~mag$ in two $20~deg^2$ fields. The project is mainly focusing on the completeness of LAMOST ExtraGAlactic Surveys (LEGAS) in the SGC, the deficiencies of source selection methods and the basic performance parameters of LAMOST telescope. In both fields, more than 95% of galaxies have been observed. A post-processing has been applied to LAMOST 1D spectrum to remove the majority of remaining sky background residuals. More than 10,000 spectra have been visually inspected to measure the redshift by using combinations of different emission/absorption features with uncertainty of $\sigma_{z}/(1+z)<0.001$. In total, there are 1528 redshifts (623 absorption and 905 emission line galaxies) in Field A and 1570 redshifts (569 absorption and 1001 emission line galaxies) in Field B have been measured. The results show that it is possible to derive redshift from low SNR galaxies with our post-processing and visual inspection. Our analysis also indicates that up to 1/4 of the input targets for a typical extra-galactic spectroscopic survey might be unreliable. The multi-wavelength data analysis shows that the majority of mid-infrared-detected absorption (91.3%) and emission line galaxies (93.3%) can be well separated by an empirical criterion of $W2-W3=2.4$. Meanwhile, a fainter sequence paralleled to the main population of galaxies has been witnessed both in $M_r$/$W2-W3$ and $M_*$/$W2-W3$ diagrams, which could be the population of luminous dwarf galaxies but contaminated by the edge-on/highly inclined galaxies ($\sim30\%$).
We study numerically large-scale magnetic field evolution and its enhancement in gaseous disks of spiral galaxies. We consider a set of models with the various spiral pattern parameters and the initial magnetic field strength with taking into account gas self-gravity and cooling/heating. In agreement with previous studies, we find out that galactic magnetic field is mostly aligned with gaseous structures, however small-scale gaseous structures (spurs and clumps) are more chaotic than the magnetic field structure. In spiral arms magnetic field strongly coexists with the gas distribution, in the inter-arm region we see filamentary magnetic field structure. Simulations reveal the presence of the small-scale irregularities of the magnetic field as well as the reversal of magnetic field at the outer edge of the large-scale spurs. We provide evidences that the magnetic field in the spiral arms has a stronger mean-field component, and there is a clear inverse correlation between gas density and plasma-beta parameter, compared to the rest of the disk with a more turbulent component of the field and an absence of correlation between gas density and plasma-beta. We show the mean field growth up to 3-10$\mu G$ in the cold gas during several rotation periods (500-800 Myr), whereas ratio between azimuthal and radial field is equal to 4/1. Mean field strength increases by a factor of 1.5-2.5 for models with various spiral pattern parameters. Random magnetic field component can reach up to 25 % from the total strength. By making an analysis of the time-depended evolution of radial Poynting flux we point out that the magnetic field strength is enhanced stronger at the galactic outskirts which is due to the radial transfer of magnetic energy by the spiral arms pushing the magnetic field outward. Our results also support the presence of sufficient conditions for development of MRI at distances >11 kpc.
The BL Lac object 3C66A is one of the most luminous extragalactic sources at
TeV $\gamma$-rays (VHE, i.e. $E >100$ GeV). Since TeV $\gamma$-ray radiation is
absorbed by the extragalactic background light (EBL), it is crucial to know the
redshift of the source in order to reconstruct its original spectral energy
distribution, as well as to constrain EBL models. However, the optical spectrum
of this BL\,Lac is almost featureless, so a direct measurement of $z$ is very
difficult; in fact, the published redshift value for this source ($z=0.444$)
has been strongly questioned. Based on EBL absorption arguments, several
constraints to its redshift, in the range $0.096 < z < 0.5$, were proposed.
Since these AGNs are hosted, typically, in early type galaxies that are
members of groups or clusters, we have analysed spectro-photometrically the
environment of 3C66A, with the goal of finding the galaxy group hosting this
blazar. This study was made using optical images of a $5.5 \times
5.5$\,arcmin$^{2}$ field centred on the blazar, and spectra of 24 sources
obtained with Gemini/GMOS-N multi-object spectroscopy.
We found spectroscopic evidence of two galaxy groups along the blazar's line
of sight: one at $z \simeq 0.020$ and a second one at $z \simeq 0.340$. The
first one is consistent with a known foreground structure, while the second
group here presented has six spectroscopically confirmed members. Their
location along a red sequence in the colour-magnitude diagram allows us to
identify 34 additional candidate members of the more distant group. The
blazar's spectrum shows broad absorption features that we identify as arising
in the intergalactic medium, thus allowing us to tentatively set a redshift
lower limit at $z_{3C66A} \ge 0.33$. As a consequence, we propose that 3C66A is
hosted in a galaxy that belongs to a cluster at $z=0.340$.
We systematically analyze X-ray variability of active galactic nuclei (AGNs) in the 7~Ms \textit{Chandra} Deep Field-South survey. On the longest timescale ($\approx~17$ years), we find only weak (if any) dependence of X-ray variability amplitudes on energy bands or obscuration. We use four different power spectral density (PSD) models to fit the anti-correlation between normalized excess variance ($\sigma^2_{\rm nxv}$) and luminosity, and obtain a best-fit power law index $\beta=1.16^{+0.05}_{-0.05}$ for the low-frequency part of AGN PSD. We also divide the whole light curves into 4 epochs in order to inspect the dependence of $\sigma^2_{\rm nxv}$ on these timescales, finding an overall increasing trend. The analysis of these shorter light curves also infers a $\beta$ of $\sim 1.3$ that is consistent with the above-derived $\beta$, which is larger than the frequently-assumed value of $\beta=1$. We then investigate the evolution of $\sigma^2_{\rm nxv}$. No definitive conclusion is reached due to limited source statistics but, if present, the observed trend goes in the direction of decreasing AGN variability at fixed luminosity toward large redshifts. We also search for transient events and find 6 notable candidate events with our considered criteria. Two of them may be a new type of fast transient events, one of which is reported here for the first time. We therefore estimate a rate of fast outbursts $\langle\dot{N}\rangle = 1.0^{+1.1}_{-0.7}\times 10^{-3}~\rm galaxy^{-1}~yr^{-1}$ and a tidal disruption event~(TDE) rate $\langle\dot{N}_{\rm TDE}\rangle=8.6^{+8.5}_{-4.9}\times 10^{-5}~\rm galaxy^{-1}~yr^{-1}$ assuming the other four long outbursts to be TDEs.
Extremely metal-poor (EMP) stars are the living fossils with records of chemical enrichment history at the early epoch of galaxy formation. By the recent large observation campaigns, statistical samples of EMP stars have been obtained. This motivates us to reconsider their classification and formation conditions. From the observed lower-limits of carbon and iron abundances of Acr(C) ~ 6 and [Fe/H]cr ~ -5 for C-enhanced EMP (CE-EMP) and C-normal EMP (CN-EMP) stars, we confirm that gas cooling by dust thermal emission is indispensable for the fragmentation of their parent clouds to form such low-mass, i.e., long-lived stars, and that the dominant grain species are carbon and silicate, respectively. We constrain the grain radius r_i^{cool} of a species i and condensation efficiency f_{ij} of a key element j as r_C^{cool}/f_{C, C} = 10 um and r_Sil^{cool}/f_{Sil, Mg} = 0.1 um to reproduce Acr(C) and [Fe/H]cr, which give a universal condition 10^{[C/H]-2.30} + 10^[Fe/H] > 10^{-5.07} for the formation of every EMP star. Instead of the conventional boundary [C/Fe] = 0.7 between CE- and CN-EMP stars, this condition suggests a physically meaningful boundary [C/Fe]_{b} = 2.30 above and below which carbon and silicate grains are dominant coolants, respectively.
We describe the use of our chemical evolution model to reproduce the abundance patterns observed in a catalog of elliptical galaxies from the SDSS DR4. The model assumes ellipticals form by fast gas accretion, and suffer a strong burst of star formation followed by a galactic wind which quenches star formation. Models with fixed IMF failed in simultaneously reproducing the observed trends with the galactic mass. So, we tested a varying IMF; contrary to the diffused claim that the IMF should become bottom heavier in more massive galaxies, we find a better agreement with data by assuming an inverse trend, where the IMF goes from being bottom heavy in less massive galaxies to top heavy in more massive ones. This naturally produces a downsizing in star formation, favoring massive stars in largest galaxies. Finally, we tested the use of the Integrated Galactic IMF, obtained by averaging the canonical IMF over the mass distribution function of the clusters where star formation is assumed to take place. We combined two prescriptions, valid for different SFR regimes, to obtain the IGIMF values along the whole evolution of the galaxies in our models. Predicted abundance trends reproduce the observed slopes, but they have an offset relative to the data. We conclude that bottom-heavier IMFs do not reproduce the properties of the most massive ellipticals, at variance with previous suggestions. On the other hand, an IMF varying with galactic mass from bottom-heavier to top-heavier should be preferred
The HeII transverse proximity effect - enhanced HeII Ly{\alpha} transmission in a background sightline caused by the ionizing radiation of a foreground quasar - offers a unique opportunity to probe the emission properties of quasars, in particular the emission geometry (obscuration, beaming) and the quasar lifetime. Building on the foreground quasar survey published in Schmidt+2017, we present a detailed model of the HeII transverse proximity effect, specifically designed to include light travel time effects, finite quasar ages, and quasar obscuration. We post-process outputs from a cosmological hydrodynamical simulation with a fluctuating HeII UV background model, plus the added effect of the radiation from a single bright foreground quasar. We vary the age $t_\mathrm{age}$ and obscured sky fractions $\Omega_\mathrm{obsc}$ of the foreground quasar, and explore the resulting effect on the HeII transverse proximity effect signal. Fluctuations in IGM density and the UV background, as well as the unknown orientation of the foreground quasar, result in a large variance of the HeII Ly{\alpha} transmission along the background sightline. We develop a fully Bayesian statistical formalism to compare far UV HeII Ly{\alpha} transmission spectra of the background quasars to our models, and extract joint constraints on $t_\mathrm{age}$ and $\Omega_\mathrm{obsc}$ for the six Schmidt+2017 foreground quasars with the highest implied HeII photoionization rates. Our analysis suggests a bimodal distribution of quasar emission properties, whereby one foreground quasar, associated with a strong HeII transmission spike, is relatively old $(22\,\mathrm{Myr})$ and unobscured $\Omega_\mathrm{obsc}<35\%$, whereas three others are either younger than $(10\,\mathrm{Myr})$ or highly obscured $(\Omega_\mathrm{obsc}>70\%)$.
We report results of 6.7 GHz methanol maser monitoring of 139 star-forming sites with the Torun 32 m radio telescope from June 2009 to February 2013. The targets were observed at least once a month, with higher cadences of 2-4 measurements per week for circumpolar objects. Nearly 80 percent of the sources display variability greater than 10 per cent on a time-scale between a week and a few years but about three quarters of the sample have only 1-3 spectral features which vary significantly. Irregular intensity fluctuation is the dominant type of variability and only nine objects show evidence for cyclic variations with periods of 120 to 416 d. Synchronised and anti-correlated variations of maser features are detected in four sources with a disc-like morphology. Rapid and high amplitude bursts of individual features are seen on 3-5 occasions in five sources. Long (>50 d to 20 months) lasting bursts are observed mostly for individual or groups of features in 19 sources and only one source experienced a remarkable global flare. A few flaring features display a strong anti-correlation between intensity and line-width that is expected for unsaturated amplification. There is a weak anti-correlation between the maser feature luminosity and variability measure, i.e. maser features with low luminosity tend to be more variable than those with high luminosity. The analysis of the spectral energy distribution and continuum radio emission reveals that the variability of the maser features increases when the bolometric luminosity and Lyman flux of the exciting object decreases. Our results support the concept of a major role for infrared pumping photons in triggering outburst activity of maser emission.
The dust properties inferred from the analysis of Planck observations in total and polarized emission challenge current dust models. We propose new dust models compatible with polarized and unpolarized data in extinction and emission for translucent lines of sight ($0.5 < A_V < 2.5$). We amended the DustEM tool to model polarized extinction and emission. We fit the spectral dependence of the mean extinction, polarized extinction, SED and polarized SED with PAHs, astrosilicates and amorphous carbon (a-C). The astrosilicate population is aligned along the magnetic field lines, while the a-C population may be aligned or not. With their current optical properties, oblate astrosilicate grains are not emissive enough to reproduce the emission to extinction polarization ratio $P_{353}/p_V$ derived with Planck data. Models using prolate astrosilicate grains with an elongation $a/b=3$ and an inclusion of 20% of porosity succeed. The spectral dependence of the polarized SED is steeper in our models than in the data. Models perform slightly better when a-C grains are aligned. A small (6%) volume inclusion of a-C in the astrosilicate matrix removes the need for porosity and perfect grain alignment, and improves the fit to the polarized SED. Dust models based on astrosilicates can be reconciled with Planck data by adapting the shape of grains and adding inclusions of porosity or a-C in the astrosilicate matrix.
Studies of low surface brightness (LSB) galaxies in nearby clusters have revealed a sub-population of extremely diffuse galaxies with central surface brightness $\mu_{0,g'}$ > 24 mag arcsec$^{-2}$ and effective radius between 1.5 kpc < R$_{e}$ < 10 kpc. The origin of these Ultra Diffuse Galaxies (UDGs) is still unclear, although several theories have been suggested. We exploit the deep g', r' and i'-band images of the Fornax Deep Survey (FDS), in order to identify LSB galaxies in the center of the Fornax cluster. We identified visually all extended structures having r'-band central surface brightness of $\mu_{0,r'}$ > 23 mag arcsec$^{-2}$. We classified the objects based on their appearance and performed 2D S\'ersic model fitting with GALFIT. We analyzed their distribution and orientations in the cluster, and studied their colors and compared the LSB galaxies in Fornax with those in other environments. Our sample consists of 205 galaxies of which 196 are LSB dwarfs (with R$_e$ < 1.5kpc) and nine are UDGs (R$_e$ > 1.5 kpc). We show that the UDGs have g'-r' colors similar to those of LSB dwarfs. The largest UDGs in our sample appear different from the other LSB galaxies, in that they are significantly more elongated and extended, whereas the smaller UDGs differ from the LSB dwarfs only by their effective radii. We do not find clear differences between the structural parameters of the UDGs in our sample and those of UDGs in other galaxy environments. We find that the dwarf LSB galaxies in our sample are less concentrated in the cluster center than the galaxies with higher surface brightness, and that their number density drops in the core of the cluster. Our findings are consistent with the small UDGs forming the tail of a continuous distribution of less extended LSB galaxies. However, the elongated and distorted shapes of the large UDGs could imply that they are tidally disturbed galaxies.
When modeling astronomical objects throughout the universe, it is important to correctly treat the limitations of the data, for instance finite resolution and sensitivity. In order to simulate these effects, and to make radiative transfer models directly comparable to real observations, we have developed an open-source Python package called the FluxCompensator that enables the post-processing of the output of 3-d Monte-Carlo radiative transfer codes, such as HYPERION. With the FluxCompensator, realistic synthetic observations can be generated by modelling the effects of convolution with arbitrary point-spread functions (PSFs), transmission curves, finite pixel resolution, noise and reddening. Pipelines can be applied to compute synthetic observations that simulate observatories, such as the Spitzer Space Telescope or the Herschel Space Observatory. Additionally, this tool can read in existing observations (e.g. FITS format) and use the same settings for the synthetic observations. In this paper, we describe the package as well as present examples of such synthetic observations.
The first hydrostatic core (FHSC) is the first stable object to form in simulations of star formation. This stage has yet to be observed definitively, although several candidate FHSCs have been reported. We have produced synthetic spectral energy distributions (SEDs) from 3D hydrodynamical simulations of pre-stellar cores undergoing gravitational collapse for a variety of initial conditions. Variations in the initial rotation rate, radius and mass lead to differences in the location of the SED peak and far-infrared flux. Secondly, we attempt to fit the SEDs of five FHSC candidates from the literature and five newly identified FHSC candidates located in the Serpens South molecular cloud with simulated SEDs. The most promising FHSC candidates are fitted by a limited number of model SEDs with consistent properties, which suggests the SED can be useful for placing constraints on the age and rotation rate of the source. The sources we consider most likely to be in FHSC phase are B1-bN, CB17-MMS, Aqu-MM1 and Serpens South candidate K242. We were unable to fit SerpS-MM22, Per-Bolo 58 and Chamaeleon-MMS1 with reasonable parameters, which indicates that they are likely to be more evolved.
We investigated stellar winds from zero/low-metallicity low-mass stars by magnetohydrodynamical simulations for stellar winds driven by Alfv\'{e}n waves from stars with mass $M_{\star}=(0.6-0.8)M_{\odot}$ and metallicity $Z=(0-1)Z_{\odot}$, where $M_{\odot}$ and $Z_{\odot}$ are the solar mass and metallicity, respectively. Alfv\'{e}nic waves, which are excited by the surface convection, travel upward from the photosphere and heat up the corona by their dissipation. For lower $Z$, denser gas can be heated up to the coronal temperature because of the inefficient radiation cooling. The coronal density of Pop.II/III stars with $Z\le 0.01Z_{\odot}$ is 1-2 orders of magnitude larger than that of the solar-metallicity star with the same mass, and as a result, the mass loss rate, $\dot{M}$, is $(4.5-20)$ times larger. The soft X-ray flux [erg cm$^{-2}$s$^{-1}$] of the Pop.II/III stars is also expected to be $\approx (1-30)$ times larger than that of the solar-metallicity counterpart owing to the larger coronal density, even though the radiation cooling efficiency [erg cm$^{3}$s$^{-1}$] is smaller. A larger fraction of the input Alfv\'{e}nic wave energy is transmitted to the corona in low $Z$ stars because they avoid severe reflection owing to the smaller density difference between the photosphere and the corona. Therefore, a larger fraction is converted to the thermal energy of the corona and the kinetic energy of the stellar wind. From this energetics argument, we finally derived a scaling of $\dot{M}$ as $\dot{M}\propto L R_{\star}^{11/9}M_{\star}^{-10/9}T_{\rm eff}^{11/2}\left[\max (Z/Z_{\odot},0.01)\right]^{-1/5}$, where $L$, $R_{\star}$, and $T_{\rm eff}$ are stellar luminosity, radius, and effective temperature, respectively.
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