We present the MATLAB code Spirality, a novel method for measuring spiral arm pitch angles by fitting galaxy images to spiral templates of known pitch. Computation time is typically on the order of 2 minutes per galaxy, assuming at least 8 GB of working memory. We tested the code using 117 synthetic spiral images with known pitches, varying both the spiral properties and the input parameters. The code yielded correct results for all synthetic spirals with galaxy-like properties. We also compared the code's results to two-dimensional Fast Fourier Transform (2DFFT) measurements for the sample of nearby galaxies defined by DMS PPak. Spirality's error bars overlapped 2DFFT's error bars for 26 of the 30 galaxies. The two methods' agreement correlates strongly with galaxy radius in pixels and also with i-band magnitude, but not with redshift, a result that is consistent with at least some galaxies' spiral structure being fully formed by z=1.2, beyond which there are few galaxies in our sample. The Spirality code package also includes GenSpiral, which produces FITS images of synthetic spirals, and SpiralArmCount, which uses a one-dimensional Fast Fourier Transform to count the spiral arms of a galaxy after its pitch is determined. The code package is freely available online; see Comments for URL.
Recent analysis of the SDSS-III/APOGEE Data Release 12 stellar catalogue has revealed that the Milky Way's metallicity distribution function (MDF) changes shape as a function of radius, transitioning from being negatively skewed at small Galactocentric radii to positively skewed at large Galactocentric radii. Using a high resolution, N-body+SPH simulation, we show that the changing skewness arises from radial migration - metal-rich stars form in the inner disk and subsequently migrate to the metal-poorer outer disk. These migrated stars represent a large fraction (> 50%) of the stars in the outer disk; they populate the high metallicity tail of the MDFs and are, in general, more metal-rich than the surrounding outer disk gas. The simulation also reproduces another surprising APOGEE result: the spatially invariant high-[alpha/Fe] MDFs. This arises in the simulation from the migration of a population formed within a narrow range of radii (3.2+/-1.2 kpc) and time (8.8+/-0.6 Gyr ago), rather than from spatially extended star formation in a homogeneous medium at early times. These results point toward the crucial role radial migration has played in shaping our Milky Way.
Filaments play a key role in the molecular clouds' evolution, but their internal dynamical properties remain poorly characterized. To further explore the physical state of these structures, we have investigated the kinematic properties of the Musca cloud. We have sampled the main axis of this filamentary cloud in $^{13}$CO and C$^{18}$O (2--1) lines using APEX observations. The different line profiles in Musca shows that this cloud presents a continuous and quiescent velocity field along its $\sim$6.5 pc of length. With an internal gas kinematics dominated by thermal motions (i.e. $\sigma_{NT}/c_s\lesssim1$) and large-scale velocity gradients, these results reveal Musca as the longest velocity-coherent, sonic-like object identified so far in the ISM. The (tran-)sonic properties of Musca present a clear departure from the predicted supersonic velocity dispersions expected in the Larson's velocity dispersion-size relationship, and constitute the first observational evidence of a filament fully decoupled from the turbulent regime over multi-parsec scales.
The mass distribution of the Galactic disk is constructed from the terminal velocity curve and the mass discrepancy-acceleration relation. Mass models numerically quantifying the detailed surface density profiles are tabulated. For $R_0 = 8$ kpc, the models have stellar mass $5 < M_* < 6 \times 10^{10}$ M$_{\odot}$, scale length $2.0 \le R_d \le 2.9$ kpc, LSR circular velocity $222 \le \Theta_0 \le 233$ km s$^{-1}$, and solar circle stellar surface density $34 \le \Sigma_d(R_0) \le 61$ M$_{\odot}$ pc$^{-2}$. The present inter-arm location of the solar neighborhood may have a somewhat lower stellar surface density than average for the solar circle. The Milky Way appears to be a normal spiral galaxy that obeys scaling relations like the Tully-Fisher relation, the size-mass relation, and the disk maximality-surface brightness relation. The stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles in the terminal velocity curve correspond to known spiral features (e.g., the Centaurus Arm is a $\sim 50\%$ overdensity). The rotation curve switches between positive and negative over scales of hundreds of parsecs. The rms amplitude $\langle$$|$$dV/dR$$|^2$$\rangle$$^{1/2} \approx 14$ km s$^{-1}$ kpc$^{-1}$, implying that commonly neglected terms in the Jeans equations may be non-negligible. The spherically averaged local dark matter density is $\rho_{0,DM} \approx 0.009$ M$_{\odot}$ pc$^{-3}$ (0.3 GeV cm$^{-3}$). Adiabatic compression of the dark matter halo may help reconcile the Milky Way with the $c$-$V_{200}$ relation expected in $\Lambda$CDM while also helping to mitigate the too big to fail problem, but it remains difficult to reconcile the inner bulge/bar dominated region with a cuspy halo. We note that NGC 3521 is a near twin to the Milky Way, having a similar luminosity, scale length, and rotation curve.
To study the accretion phase for local massive galaxies, we search accreting satellites around a massive compact galaxy (M_*~3.9x10^10Msun), spectroscopically confirmed (z_spec-1.9213) in the eXtreme Deep Field, which has been originally reported in Szomoru et al. We detect 1369 satellite candidates within the projected virial radius (rvir~300 kpc) of the compact galaxy in the all-combined ACS image with 5sigma-limiting magnitude of mACS~30.6 ABmag, which corresponds to ~1.6x10^7M_sun at the redshift. The photometric redshift measured with 12 multi-band images confirms 34 satellites out of the candidates. Most of the satellites are found to have the rest-frame colors consistent with star forming galaxies. We investigate the relation between stellar mass and star formation rate (the star formation main sequence), and find the steeper slope at the low-mass end (<10^8M_sun), while more massive satellites are consistently on the sequence reported in previous studies. Within the uncertainties of star formation and photometric redshift, we conjecture possible scenarios for the compact galaxy which evolves to a local massive galaxy by way of significant size and mass growth. While merging of the existing total stellar mass of the satellites is not enough to explain the mass growth predicted by observations and simulations, the contribution by in-situ star formation in the satellites would compensate the deficit. Provided that most satellites keep the observed in-situ star formation and then quench before they accrete by, e.g., environmental quenching, the compact galaxy would become a massive early-type galaxy consistent with the local size-mass relation.
We study an inherent length scale of galactic halos in the Bose-Einstein
condensate (or scalar field) dark matter model. Considering evolution of the
density perturbation we show that the average background matter density
determines a quantum Jeans mass and hence the spatial size of galaxies. In this
model the minimum size of galaxies increases, while the minimum mass of the
galaxies decreases as the universe evolves. The observed values of the mass and
the size of the dwarf galaxies are successfully reproduced with the dark matter
particle mass $m\simeq 5\times 10^{-22}eV$. The rotation velocity of dwarf
galaxies is $O(\sqrt{H/m}$) c, where $H$ is the Hubble parameter.
We also suggest that ultra compact dwarf galaxies are remnants of dwarf
galaxies formed in the early universe.
The mass discrepancy acceleration relation (MDAR) describes the coupling between baryons and dark matter (DM) in galaxies: the ratio of total-to-baryonic mass at a given radius anti-correlates with the acceleration due to baryons. The MDAR has been seen as a challenge to the $\Lambda$CDM galaxy formation model, while it can be explained by Modified Newtonian Dynamics. In this Letter we show that the MDAR arises in a $\Lambda$CDM cosmology once observed galaxy scaling relations are taken into account. We build semi-empirical models based on $\Lambda$CDM haloes, with and without the inclusion of baryonic effects, coupled to empirically motivated structural relations. Our models can reproduce the MDAR: specifically, a mass-dependent density profile for DM haloes can fully account for the observed MDAR shape, while a universal profile shows a discrepancy with the MDAR of dwarf galaxies with $\rm M^{\star}$$<$$\rm10^{9.5}M_{\odot}$, a further indication suggesting the existence of DM cores. Additionally, we reproduce slope and normalization of the baryonic Tully-Fisher relation (BTFR) with 0.17 dex scatter. These results imply that in $\Lambda$CDM (i) the MDAR is driven by structural scaling relations of galaxies and DM density profile shapes, and (ii) the baryonic fractions determined by the BTFR are consistent with those inferred from abundance-matching studies.
In this analysis we illustrate how the relatively new emission mechanism known as spinning dust can be used to characterize dust grains in the interstellar medium. We demonstrate this by using spinning dust emission observations to constrain the abundance of very small dust grains (a $\lesssim$ 10nm) in a sample of Galactic cold cores. Using the physical properties of the cores in our sample as inputs to a spinning dust model, we predict the expected level of emission at a wavelength of 1cm for four different very small dust grain abundances, which we constrain by comparing to 1cm CARMA observations. For all of our cores we find a depletion of very small grains, which we suggest is due to the process of grain growth. This work represents the first time that spinning dust emission has been used to constrain the physical properties of interstellar dust grains.
We present calculated rate coefficients for ro-vibrational transitions of CO in collisions with H atoms for a gas temperature range of 10 K $\leq T \leq$ 3000 K, based on the recent three-dimensional ab initio H-CO interaction potential of Song et al(2013). Rate coefficients for ro-vibrational $v=1,j=0-30 \rightarrow v'=0, j'$ transitions were obtained from scattering cross sections previously computed with the close-coupling method by Song et al(2015). Combining these with the rate coefficients for vibrational $v=1-5 \rightarrow v' < v$ quenching obtained with the infinite-order sudden approximation, we propose a new extrapolation scheme that yields the rate coefficients for ro-vibrational $v=2-5,j=0-30 \rightarrow v',j'$ de-excitation. Cross sections and rate coefficients for ro-vibrational $v=2, j=0-30 \rightarrow v'=1,j'$ transitions calculated with the close-coupling method confirm the effectiveness of this extrapolation scheme. Our calculated and extrapolated rates are very different from those that have been adopted in the modeling of many astrophysical environments. The current work provides the most comprehensive and accurate set of ro-vibrational de-excitation rate coefficients for the astrophysical modeling of the H-CO collision system. Application of the previously available and new data sets in astrophysical slab models shows that the line fluxes typically change by 20-70% in high temperature environments (800 K) with an H/H$_2$ ratio of 1; larger changes occur for lower temperatures.
How a galaxy regulates its SNe energy into different interstellar/circumgalactic medium components strongly affects galaxy evolution. Based on the JVLA D-configuration C- (6 GHz) and L-band (1.6 GHz) continuum observations, we perform statistical analysis comparing multi-wavelength properties of the CHANG-ES galaxies. The high-quality JVLA data and edge-on orientation enable us for the first time to include the halo into the energy budget for a complete radio-flux-limited sample. We find tight correlations of $L_{\rm radio}$ with the mid-IR-based SFR. The normalization of our $I_{\rm 1.6GHz}/{\rm W~Hz^{-1}}-{\rm SFR}$ relation is $\sim$2-3 times of those obtained for face-on galaxies, probably a result of enhanced IR extinction at high inclination. We also find tight correlations between $L_{\rm radio}$ and the SNe energy injection rate $\dot{E}_{\rm SN(Ia+CC)}$, indicating the energy loss via synchrotron radio continuum accounts for $\sim0.1\%$ of $\dot{E}_{\rm SN}$, comparable to the energy contained in CR electrons. The integrated C-to-L-band spectral index is $\alpha\sim0.5-1.1$ for non-AGN galaxies, indicating a dominance by the diffuse synchrotron component. The low-scatter $L_{\rm radio}-{\rm SFR}$/$L_{\rm radio}-\dot{E}_{\rm SN (Ia+CC)}$ relationships have super-linear logarithmic slopes at $\sim2~\sigma$ in L-band ($1.132\pm0.067$/$1.175\pm0.102$) while consistent with linear in C-band ($1.057\pm0.075$/$1.100\pm0.123$). The super-linearity could be naturally reproduced with non-calorimeter models for galaxy disks. Using Chandra halo X-ray measurements, we find sub-linear $L_{\rm X}-L_{\rm radio}$ relations. These results indicate that the observed radio halo of a starburst galaxy is close to electron calorimeter, and a galaxy with higher SFR tends to distribute an increased fraction of SNe energy into radio emission (than X-ray).
In the earliest phases of star-forming clouds, stable molecular species, such as CO, are important coolants in the gas phase. Depletion of these molecules on dust surfaces affects the thermal balance of molecular clouds and with that their whole evolution. For the first time, we study the effect of grain surface chemistry (GSC) on star formation and its impact on the initial mass function (IMF). We follow a contracting translucent cloud in which we treat the gas-grain chemical interplay in detail, including the process of freeze-out. We perform 3d hydrodynamical simulations under three different conditions, a pure gas-phase model, a freeze-out model, and a complete chemistry model. The models display different thermal evolution during cloud collapse. The equation of state (EOS) of the gas becomes softer with CO freeze-out and the results show that at the onset of star formation, the cloud retains its evolution history such that the number of formed stars differ (by 7%) between the three models. While the stellar mass distribution results in a different IMF when we consider pure freeze-out, with the complete treatment of the GSC, the divergence from a pure gas-phase model is minimal. We find that the impact of freeze-out is balanced by the non-thermal processes; chemical and photodesorption. We also find an average filament width of 0.12 pc ($\pm$0.03 pc), and speculate that this may be a result from the changes in the EOS caused by the gas-dust thermal coupling. We conclude that GSC plays a big role in the chemical composition of molecular clouds and that surface processes are needed to accurately interpret observations, however, that GSC does not have a significant impact as far as star formation and the IMF is concerned.
In this study we present high resolution VIMOS-IFU spectroscopy of the extremely metal-poor HII/blue compact dwarf (BCD) galaxy Tol 65. The optical appearance of this galaxy shows clearly a cometary morphology with a bright main body and an extended and diffuse stellar tail. We focus on the detection of metallicity gradients or inhomogeneities as expected if the ongoing star-formation activity is sustained by the infall/accretion of metal-poor gas. No evidences of significant spatial variations of abundances were found within our uncertainties. However, our findings show a slight anticorrelation between gas metallicity and star-formation rate at spaxel scales, in the sense that high star-formation is found in regions of low-metallicity, but the scatter in this relation indicates that the metals are almost fully diluted. Our observations show the presence of extended H$\alpha$ emission in the stellar tail of the galaxy. We estimated that the mass of the ionized gas in the tail M(HII)$_{tail} \sim$1.7$\times$10$^5$ M$_{\odot}$ corresponds with $\sim$ 24\% of the total mass of the ionized gas in the galaxy. We found that the H$\alpha$ velocity dispersion of the main body and the tail of the galaxy are comparable with the one found in the neutral gas by previous studies. This suggests that the ionized gas still retains the kinematic memory of its parental cloud and likely a common origin. Finally, we suggest that the infall/accretion of cold gas from the outskirts of the galaxy and/or minor merger/interaction may have produced the almost flat abundance gradient and the cometary morphology in Tol 65.
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We study the relationship between the X-ray luminosity and star formation rate (SFR) in an unbiased sample of dusty active galactic nuclei (AGNs), detected in both the hard X-ray and far-infrared (IR) bands in the XMM-LSS field. The sample consists of 451 AGNs with spectroscopic redshifts of 0.04 < z <3.3, and spans an X-ray luminosity range of L(2-10keV)=10^41-45 erg/s. We find a positive correlation between the X-ray luminosity and SFR derived from AGN-removed IR luminosity. We find that binning the sample by SFR instead of LX results in a more positive correlation. This is consistent with the scenario in which the shorter variability time scale of AGN than star formation flattens the observed correlation between AGN and star formation. We do not find significant diversity in the observed correlation when considering subsets selected based on supermassive black hole mass or Eddington ratio, indicating that AGN accretion has at most a limited effect on the SFR-Lx relation. Comparing to results in the literature, we propose a picture in which the correlation depends on sample composition. Additionally, we find a constant ratio between the SFR and the black hole accretion rate (BHAR) of log(SFR/BHAR)=(3.03+/-0.55). This value coincides with the ratio between galaxy bulge/total stellar mass and SMBH mass found in the local universe. Our results are consistent with the secular evolution scenario, in which dusty AGNs are coevolving with the host from the same gas supply at a constant rate regardless of accretion activity.
Medium resolution (R=4,000 to 9,000) spectra of the near infrared Ca II lines (at 8498, 8542, and 8662 A) in M31 globular cluster integrated light spectra are presented. In individual stars the Ca II triplet (CaT) traces stellar metallicity; this paper compares integrated CaT strengths to well determined, high precision [Fe/H] values from high resolution integrated light spectra. The target globular clusters cover a wide range in metallicity (from [Fe/H] = -2.1 to -0.2). While most are older than 10 Gyr, some may be of intermediate age (2-6 Gyr). A handful (3-6) have detailed abundances (e.g. low [Ca/Fe]) that indicate they may have been accreted from dwarf galaxies. Using various measurements and definitions of CaT strength, it is confirmed that for GCs with [Fe/H] < -0.4 and older than 2 Gyr the integrated CaT traces cluster [Fe/H] to within about 0.2 dex, independent of age. CaT lines in metal rich GCs are very sensitive to nearby atomic lines (and TiO molecular lines in the most metal rich GCs), largely due to line blanketing in continuum regions. The [Ca/Fe] ratio has a mild effect on the integrated CaT strength in metal poor GCs. The integrated CaT can therefore be safely used to determine rough metallicities for distant, unresolved clusters, provided that attention is paid to the limits of the measurement techniques.
We present multi-wavelength detections of nine candidate gravitationally-lensed dusty star-forming galaxies (DSFGs) selected at 218 GHz ($\sim$1.4 mm) from the ACT equatorial survey. These represent the subset of the total ACT sample lying in Herschel SPIRE fields, and all nine of the 218 GHz detections were found to have bright Herschel counterparts. By fitting their spectral energy distributions (SEDs) with a modified blackbody model with power-law temperature distribution, we find the sample has a median redshift of $z=4.1^{+1.1}_{-1.0}$ (68 percent confidence interval), as expected for 218 GHz selection, and an apparent total infrared luminosity of $\log_{10}({\mu L_{\rm IR}}/L_\odot) = 13.32^{+0.25}_{-0.19}$, which suggests that they are either strongly lensed sources with magnification $\mu=5-10$ or unresolved collections of unlensed DSFGs. The effective apparent diameter of the sample is $ {\sqrt{\mu}\,d} \sim 4.2^{+1.7}_{-1.0}$ kpc, further evidence of strong lensing or multiplicity as the typical diameter of dusty star-forming galaxies is $1-3$ kpc. Additionally, we find that the sources have substantial optical depth ($\tau = 4.2^{+3.7}_{-1.9}$) around the peak in the modified blackbody spectrum ($\lambda_{\rm obs} \le 500$ $\mu$m).
The joint catalogue of Active Galactic Nuclei selected from optical identifications of X-ray sources was created as a combination of two samples: Hamburg-ROSAT Catalogue (HRC) and Byurakan-Hamburg-ROSAT Catalogue (BHRC). Both are based on optical identifications of X-ray sources from ROSAT catalogues using low-dispersion spectra of Hamburg Quasar Survey (HQS). However, HRC and BHRC contain a number of misidentifications and using the recent optical and multiwavelength (MW) catalogues we have revised both samples excluding false AGN and adding new genuine ones. Thus a new large homogeneous complete sample of 4253 X-ray selected AGN was created. 3352 of them are listed in the Catalogue of QSOs and Active Galaxies and 387 also are in Roma Multifrequency Catalogue of Blazars. 901 candidate AGN are subject for further study. We classified 173 of these objects using their SDSS DR12 spectra. Following activity types were revealed: 61 AGN, 21 HII galaxies, 12 emission-line galaxies without definite type, 71 absorption-line galaxies, 2 stars, and 6 were classified as "Unknown". A special emphasis is made on narrow-line Sy1.0-Sy1.5 galaxies and QSOs, as many of them have soft X-ray, strong FeII lines, and relatively narrow lines coming from BLR ("narrow broad lines"). As a result, the sample of genuine AGN was enlarged to 3413 objects. We have retrieved MW data from recent catalogues and carried out statistical investigations for the whole AGN sample. An attempt to find connections between fluxes in different bands for different types of sources, and identify their characteristics thus confirming candidate AGNs have been carried out. We have analyzed X-ray properties of these sources to find a limit between normal galaxies and X-ray AGN.
We present a new photometric catalogue of the rich globular cluster (GC) system around M87, the brightest cluster galaxy in Virgo. Using archival Next Generation Virgo cluster Survey (NGVS) images in the ugriz bands, observed with CFHT/MegaPrime, we perform a careful subtraction of the galaxy's halo light in order to detect objects at small galactocentric radii as well as in the wider field, and find 17620 GC candidates over a radius range from 1.3 kpc to 445 kpc with g < 24 magnitudes. By inferring their colour, radial and magnitude distributions in a Bayesian way, we find that they are well described as a mixture of two GC populations and two distinct contaminant populations, but confirm earlier findings of radius-dependent colour gradients in both GC populations. This is consistent with a picture in which the more enriched GCs reside deeper in the galaxy's potential well, indicating a role for dissipative collapse in the formation of both the red and the blue GCs.
We investigate evolution of clumpy galaxies with the Hubble Space Telescope (HST) samples of ~190,000 photo-z and Lyman break galaxies at z~0-8. We detect clumpy galaxies with off-center clumps in a self-consistent algorithm that is well tested with previous study results, and measure the number fraction of clumpy galaxies at the rest-frame UV, f_clumpy^UV. We identify an evolutionary trend of f_clumpy^UV over z~0-8 for the first time: f_clumpy^UV increases from z~8 to z~1-3 and subsequently decreases from z~1 to z~0, which follows the trend of Madau-Lilly plot. A low average Sersic index of n~1 is found in the underlining components of our clumpy galaxies at z~0-2, indicating that typical clumpy galaxies have disk-like surface brightness profiles. Our f_clumpy^UV values correlate with physical quantities related to star formation activities for star-forming galaxies at z~0-7. We find that clump colors tend to be red at a small galactocentric distance for massive galaxies with log(M_*/M_sun)>~11. All of these results are consistent with a picture that a majority of clumps form in the violent disk instability and migrate into the galactic centers.
In this paper, we try to explain the observed correlation between the covering factor (CF) of hot dust and the properties of active galactic nuclei (AGNs), e.g., the bolometric luminosity ($L_{\rm{bol}}$) and black hole mass ($M_{\rm{BH}}$). Combining the possible dust distribution in the torus, the angular dependence of the radiation of the accretion disc, and the relation between the critical angle of torus and the Eddington ratio, there are eight possible models investigated in our work. We fit the observed CF with these models to determine the parameters of them. As a result, clumpy torus models can generally explain the observed correlations of tori, while the smooth models fail to produce the required CFs. However, there is still significant scatter even for the best-fitting model, which is the combination of a clumpy torus illuminated by the anisotropic radiation of accretion disc in an AGN. Although some of the observed scatter is due to the uncertainties in measuring $L_{\rm{bol}}$ and $M_{\rm{BH}}$, other factors are required in more realistic model. The models examined in this paper are not necessary to be the physical model of tori. However, the reasonable assumptions selected during this process should be helpful in constructing physical models of tori.
We highlight distinct and systematic observational features of magnetic field morphologies in polarized submm dust continuum. We illustrate this with specific examples and show statistical trends from a sample of 50 star-forming regions.
Here we investigate light curves of the continuum and emission lines of five type 1 active galactic nuclei (AGN) from our monitoring campaign, to test time-evolution of their time delays.Using both modeled and observed AGN light curves we apply Gaussian-kernel based estimator to capture variation of local patterns of their time evolving delays. The largest variations of time delays of all objects occur in the period when continuum or emission lines luminosity is the highest. However, Gaussian kernel based method shows instability in the case of NGC 5548, 3C 390.3, E1821+643 and NGC 4051 possible due to numerical discrepancies between Damped Random Walk (DRW) time scale of light curves and sliding time windows of the method. The temporal variations of time lags of Arp 102B can correspond to the real nature of the time lag evolution.
[Oiii]{\lambda}{\lambda}4959,5007 "blue outliers" -- that are suggestive of outflows in the narrow line region of quasars -- appear to be much more common at intermediate z (high luminosity) than at low z. About 40% of quasars in a Hamburg ESO intermediate-z sample of 52 sources qualify as blue outliers (i.e., quasars with [OIII] {\lambda}{\lambda}4959,5007 lines showing large systematic blueshifts with respect to rest frame). We discuss major findings on what has become an intriguing field in active galactic nuclei research and stress the relevance of blue outliers to feedback and host galaxy evolution.
We observed the Seyfert 1 galaxy NGC 985 on multiple occasions to search for variability in its UV and X-ray absorption features in order to establish their location and physical properties. We use XMM-Newton to obtain X-ray spectra using the EPIC-pn camera, and the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) to obtain UV spectra. Our observations are simultaneous and span timescales of days to years. We find that the soft X-ray obscuration that absorbed the low energy continuum of NGC 985 in August 2013 diminished greatly by January 2015. The total X-ray column density decreased from 2.1 x 10^22 cm^-2 to ~6 x 10^21 cm^-2. We also detect broad, fast UV absorption lines in COS spectra obtained during the 2013 obscuration event. Lines of C III*, Ly alpha, Si IV and C IV with outflow velocities of -5970 km/s and a full-width at half-maximum of 1420 km/s are prominent in the 2013 spectrum, but have disappeared in all but Ly alpha in the 2015 spectra. The ionization state and the column density of the UV absorbing gas is compatible with arising in the same gas as that causing the X-ray obscuration. The high velocity of the UV-absorbing gas suggests that the X-ray obscurer and the associated UV outflow are manifestations of an accretion disk wind.
A simple one-dimensional model of CH$_3$OH maser is considered. Two techniques are used for the calculation of molecule level populations: the accelerated lambda iteration (ALI) method and the large velocity gradient (LVG), or Sobolev, approximation. The LVG approximation gives accurate results provided that the characteristic dimensions of the medium are larger than 5-10 lengths of the resonance region. We presume that this condition can be satisfied only for the largest observed maser spot distributions. Factors controlling the pumping of class I and class II methanol masers are considered.
Atacama Large Millimeter/submillimeter Array (ALMA) 12CO(J=1-0) observations are used to study the cold molecular ISM of the Cartwheel ring galaxy and its relation to HI and massive star formation (SF). CO moment maps find $(2.69\pm0.05)\times10^{9}$ M$_{\odot}$ of H$_2$ associated with the inner ring (72%) and nucleus (28%) for a Galactic I(CO)-to-N(H2) conversion factor ($\alpha_{\rm CO}$). The spokes and disk are not detected. Analysis of the inner ring's CO kinematics show it to be expanding ($V_{\rm exp}=68.9\pm4.9$ km s$^{-1}$) implying an $\approx70$ Myr age. Stack averaging reveals CO emission in the starburst outer ring for the first time, but only where HI surface density ($\Sigma_{\rm HI}$) is high, representing $M_{\rm H_2}=(7.5\pm0.8)\times10^{8}$ M$_{\odot}$ for a metallicity appropriate $\alpha_{\rm CO}$, giving small $\Sigma_{\rm H_2}$ ($3.7$ M$_{\odot}$ pc$^{-2}$), molecular fraction ($f_{\rm mol}=0.10$), and H$_2$ depletion timescales ($\tau_{\rm mol} \approx50-600$ Myr). Elsewhere in the outer ring $\Sigma_{\rm H_2}\lesssim 2$ M$_{\odot}$ pc$^{-2}$, $f_{\rm mol}\lesssim 0.1$ and $\tau_{\rm mol}\lesssim 140-540$ Myr (all $3\sigma$). The inner ring and nucleus are H$_2$-dominated and are consistent with local spiral SF laws. $\Sigma_{\rm SFR}$ in the outer ring appears independent of $\Sigma_{\rm H_2}$, $\Sigma_{\rm HI}$ or $\Sigma_{\rm HI+H_2}$. The ISM's long confinement in the robustly star forming rings of the Cartwheel and AM0644-741 may result in either a large diffuse H$_2$ component or an abundance of CO-faint low column density molecular clouds. The H$_2$ content of evolved starburst rings may therefore be substantially larger. Due to its lower $\Sigma_{\rm SFR}$ and age the Cartwheel's inner ring has yet to reach this state. Alternately, the outer ring may trigger efficient SF in an HI-dominated ISM.
The Sun lies in the middle of an enormous cavity of a million degree gas, known as the Local Bubble. The Local Bubble is surrounded by a wall of denser neutral and ionized gas. The Local Bubble extends around 100 pc in the plane of Galaxy and hundreds of parsecs vertically, but absorption-line surveys of neutral sodium and singly-ionized calcium have revealed a highly irregular structure and the presence of neutral clouds within an otherwise tenuous and hot gas. We have undertaken an all-sky, European-Iranian survey of the Local Bubble in the absorption of a number of diffuse interstellar bands (DIBs) to offer a novel view of our neighbourhood. Our dedicated campaigns with ESO's New Technology Telescope and the ING's Isaac Newton Telescope comprise high signal-to-noise, medium-resolution spectra, concentrating on the 5780 and 5797 \AA\ bands which trace ionized/irradiated and neutral/shielded environments, respectively; their carriers are unknown but likely to be large carbonaceous molecules. With about 660 sightlines towards early-type stars distributed over distances up to about 200 pc, our data allow us to reconstruct the first ever 3D DIB map of the Local Bubble, which we present here. While we confirm our expectations that the 5780 \AA\ DIB is relatively strong compared to the 5797 \AA\ DIB in hot/irradiated regions such as which prevail within the Local Bubble and its walls, and the opposite is true for cooler/shielded regions beyond the confines of the Local Bubble, we unexpectedly also detect DIB cloudlets inside of the Local Bubble. These results reveal new insight into the structure of the Local Bubble, as well as helping constrain our understanding of the carriers of the DIBs.
Optically bright, wide separation double (gravitationally lensed) quasars can be easily monitored, leading to light curves of great importance in determining the Hubble constant and other cosmological parameters, as well as the structure of active nuclei and halos of galaxies. Searching for new double quasars in the SDSS-III database, we discovered SDSS J1442+4055. This consists of two bright images (18-19 magnitudes in the r band) of the same distant quasar at redshift z = 2.575. The two quasar images are separated by about 2.1 arcsec, show significant parallel flux variations and can be monitored from late 2015. We also found other two double quasar candidates, SDSS J1617+3827 (z = 2.079) and SDSS J1642+3200 (z = 2.264), displaying evidence for the presence of a lensing object and parallel flux variations, but requiring further spectroscopic observations to be confirmed as lensed quasars.
We present an analysis of galaxies in groups and clusters at $0.8<z<1.2$, from the GCLASS and GEEC2 spectroscopic surveys. We compute a "conversion fraction" $f_{\rm convert}$ that represents the fraction of galaxies that were prematurely quenched by their environment. For massive galaxies, $M_{\rm star}>10^{10.3}M_\odot$, we find $f_{\rm convert}\sim 0.4$ in the groups and $\sim 0.6$ in the clusters, similar to comparable measurements at $z=0$. This means the time between first accretion into a more massive halo and final star formation quenching is $t_p\sim 2$ Gyr. This is substantially longer than the estimated time required for a galaxy's star formation rate to become zero once it starts to decline, suggesting there is a long delay time during which little differential evolution occurs. In contrast with local observations we find evidence that this delay timescale may depend on stellar mass, with $t_p$ approaching $t_{\rm Hubble}$ for $M_{\rm star}\sim 10^{9.5}M_\odot$. The result suggests that the delay time must not only be much shorter than it is today, but may also depend on stellar mass in a way that is not consistent with a simple evolution in proportion to the dynamical time. Instead, we find the data are well-matched by a model in which the decline in star formation is due to "overconsumption", the exhaustion of a gas reservoir through star formation and expulsion via modest outflows in the absence of cosmological accretion. Dynamical gas removal processes, which are likely dominant in quenching newly accreted satellites today, may play only a secondary role at $z=1$.
We measure carbon radio recombination line (RRL) emission at 5.3 GHz toward four HII regions with the Green Bank Telescope (GBT) to determine the magnetic field strength in the photodissociation region (PDR) that surrounds the ionized gas. Roshi (2007) suggests that the non-thermal line widths of carbon RRLs from PDRs are predominantly due to magneto-hydrodynamic (MHD) waves, thus allowing the magnetic field strength to be derived. We model the PDR with a simple geometry and perform the non-LTE radiative transfer of the carbon RRL emission to solve for the PDR physical properties. Using the PDR mass density from these models and the carbon RRL non-thermal line width we estimate total magnetic field strengths of B ~ 100-300 micro Gauss in W3 and NGC6334A. Our results for W49 and NGC6334D are less well constrained with total magnetic field strengths between B ~ 200-1000 micro Gauss. HI and OH Zeeman measurements of the line-of-sight magnetic field strength (B_los), taken from the literature, are between a factor of ~0.5-1 of the lower bound of our carbon RRL magnetic field strength estimates. Since |B_los| <= B, our results are consistent with the magnetic origin of the non-thermal component of carbon RRL widths.
The presence and abundance of the short-lived radioisotopes (SLRs) $^{26}$Al
and $^{60}$Fe during the formation of the Solar System is difficult to explain
unless the Sun formed in the vicinity of one or more massive star(s) that
exploded as supernovae. Two different scenarios have been proposed to explain
the delivery of SLRs to the protosolar nebula: (i) direct pollution of the
protosolar disc by supernova ejecta and (ii) the formation of the Sun in a
sequential star formation event in which supernovae shockwaves trigger further
star formation which is enriched in SLRs.
The sequentially triggered model has been suggested as being more
astrophysically likely than the direct pollution scenario. In this paper we
investigate this claim by analysing a combination of $N$-body and SPH
simulations of star formation. We find that sequential star formation would
result in large age spreads (or even bi-modal age distributions for spatially
coincident events) due to the dynamical relaxation of the first star-formation
event(s). Secondly, we discuss the probability of triggering spatially and
temporally discrete populations of stars and find this to be only possible in
very contrived situations. Taken together, these results suggest that the
formation of the Solar System in a triggered star formation event is as
improbable, if not more so, than the direct pollution of the protosolar disc by
a supernova.
We present a new method to identify luminous off-nuclear X-ray sources in the outskirts of galaxies from large public redshift surveys, distinguishing them from foreground and background interlopers. Using the 3XMM-DR5 catalog of X-ray sources and the SDSS DR12 spectroscopic sample of galaxies, with the help of this off-nuclear cross-matching technique, we selected 98 sources with inferred X-ray luminosities in the range $10^{41} < L_{\rm X} < 10^{44}\,{\rm erg\,s}^{-1}$, compatible with hyperluminous X-ray objects (HLX). To validate the method, we verify that it allowed us to recover known HLX candidates such as ESO 243$-$49 HLX$-$1 and M82 X$-$1. From a statistical study, we conservatively estimate that up to $71 \pm 11$ of these sources may be fore- or background sources, statistically leaving at least 16 that are likely to be HLXs, thus providing support for the existence of the HLX population. We identify two good HLX candidates and using other publicly available datasets, in particular the VLA FIRST in radio, UKIDSS in the near-infrared, GALEX in the ultra-violet and CFHT Megacam archive in the optical, we present evidence that these objects are unlikely to be foreground or background X-ray objects of conventional types, e.g. active galactic nuclei, BL Lac objects, Galactic X-ray binaries or nearby stars. However, additional dedicated X-ray and optical observations are needed to confirm their association with the assumed host galaxies and thus secure their HLX classification.
Utilizing the high-resolution, large-scale LAOZI cosmological simulations we investigate the nature of the metal-poor (${\rm [Z/H]<-2}$) damped Lyman alpha systems (mpDLA) at $z=3$. The following physical picture of mpDLAs emerges. The majority of mpDLAs inhabit regions $\ge 20$~kpc from the host galaxy center on infalling cold gas streams originating from the intergalactic medium, with infall velocity of $\sim 100$ km/s and temperature of $\sim 10^{4}$ K. For each host galaxy, on average, about $1\%$ of the area within a radius $150$~kpc is covered by mpDLAs. The mpDLAs are relatively diffuse ($n_{\rm{gas}} \sim 10^{-2}$ cm$^{-3}$), Jeans quasi-stable, and have very low star formation rate ($\dot{\Sigma} \le 10^{-4} \msun \rm{\ yr}^{-1} \rm{\ kpc}^{-2}$). As mpDLAs migrate inward to the galaxy center, they mix with high metallicity gas and stellar outflows in the process, removing themselves from the metal-poor category and rendering the central ($\le 5$ kpc) regions of galaxies devoid of mpDLAs. Thus, the central regions of the host galaxies are populated by mostly metal-rich DLAs instead of mpDLAs. All observables of the simulated mpDLAs are in excellent agreement with observations, except the gas density, which is about a factor of ten lower than the value inferred observationally. However, the observationally inferred value is based on simplified assumptions that are not borne out in the simulations.
Sensitive ground-based submillimeter surveys, such as ATLASGAL, provide a global view on the distribution of cold dense gas in the Galactic plane. Here we use the 353 GHz maps from the Planck/HFI instrument to complement the ground-based APEX/LABOCA observations with information on larger angular scales. The resulting maps reveal the distribution of cold dust in the inner Galaxy with a larger spatial dynamic range. We find examples of elongated structures extending over angular scales of 0.5 degree. Corresponding to >30 pc structures in projection at a distance of 3 kpc, these dust lanes are very extended and show large aspect ratios. Furthermore, we assess the fraction of dense gas ($f_{\rm DG}$), and estimate 2-5% (above A$_{\rm{v}}>$7 mag) on average in the Galactic plane. PDFs of the column density reveal the typically observed log-normal distribution for low- and exhibit an excess at high column densities. As a reference for extragalactic studies, we show the line-of-sight integrated N-PDF of the inner Galaxy, and derive a contribution of this excess to the total column density of $\sim2.2$%, above $N_{\rm H_2} = 2.92\times10^{22}$ cm$^{-2}$. Taking the total flux density, we provide an independent estimate of the mass of molecular gas in the inner Galaxy of $\sim1\times10^9\,M_{\odot}$, which is consistent with previous estimates using CO emission. From the mass and $f_{\rm DG}$ we estimate a Galactic SFR of $\dot M = 1.3\,M_{\odot}$ yr$^{-1}$. While the distribution of diffuse gas is homogenous in the inner Galaxy, the CMZ stands out with a higher dense gas fraction. The low star formation efficiency of the Milky Way is well explained by the low $f_{\rm DG}$ in the Galactic ISM, while the high $f_{\rm DG}$ towards the CMZ, despite its low star formation activity, suggests that, in that particular region of our Galaxy, high-density gas is not the bottleneck for star formation.
Recent all-sky and large-area astronomical surveys and their catalogued data over the whole range of electromagnetic spectrum are reviewed, from Gamma-ray to radio, such as Fermi-GLAST and INTEGRAL in Gamma-ray, ROSAT, XMM and Chandra in X-ray, GALEX in UV, SDSS and several POSS I and II based catalogues (APM, MAPS, USNO, GSC) in optical range, 2MASS in NIR, WISE and AKARI IRC in MIR, IRAS and AKARI FIS in FIR, NVSS and FIRST in radio and many others, as well as most important surveys giving optical images (DSS I and II, SDSS, etc.), proper motions (Tycho, USNO, Gaia), variability (GCVS, NSVS, ASAS, Catalina, Pan-STARRS) and spectroscopic data (FBS, SBS, Case, HQS, HES, SDSS, CALIFA, GAMA). An overall understanding of the coverage along the whole wavelength range and comparisons between various surveys are given: galaxy redshift surveys, QSO/AGN, radio, Galactic structure, and Dark Energy surveys. Astronomy has entered the Big Data era. Astrophysical Virtual Observatories and Computational Astrophysics play an important role in using and analysis of big data for new discoveries.
Daily X-ray flaring represents an enigmatic phenomenon of Sgr A$^{\star}$ --- the supermassive black hole at the center of our Galaxy. We report initial results from a systematic X-ray study of this phenomenon, based on extensive {\it Chandra} observations obtained from 1999 to 2012, totaling about 4.5 Ms. We detect flares, using a combination of the maximum likelihood and Markov Chain Monte Carlo methods, which allow for a direct accounting for the pile-up effect in the modeling of the flare lightcurves and an optimal use of the data, as well as the measurements of flare parameters, including their uncertainties. A total of 82 flares are detected. About one third of them are relatively faint, which were not detected previously. The observation-to-observation variation of the quiescent emission has an average root-mean-square of $6\%-14\%$, including the Poisson statistical fluctuation of faint flares below our detection limits. We find no significant long-term variation in the quiescent emission and the flare rate over the 14 years. In particular, we see no evidence of changing quiescent emission and flare rate around the pericenter passage of the S2 star around 2002. We show clear evidence of a short-term clustering for the ACIS-S/HETG 0th-order flares on time scale of $20-70$ ks. We further conduct detailed simulations to characterize the detection incompleteness and bias, which is critical to a comprehensive follow-up statistical analysis of flare properties. These studies together will help to establish Sgr A$^{\star}$ as a unique laboratory to understand the astrophysics of prevailing low-luminosity black holes in the Universe.
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The dust in nearby galaxies absorbs a fraction of the UV-optical-near-infrared radiation produced by stars. This energy is consequently re-emitted in the infrared. We investigate the fraction of the stellar radiation absorbed by spiral galaxies from the HRS by modelling their UV-to-submillimetre spectral energy distributions. Our models provide an attenuated and intrinsic SED from which we find that on average 32 % of all starlight is absorbed by dust. We define the UV heating fraction as the fraction of dust luminosity that comes from absorbed UV photons and find that this is 56 %, on average. This percentage varies with morphological type, with later types having significantly higher UV heating fractions. We find a strong correlation between the UV heating fraction and specific star formation rate and provide a power-law fit. Our models allow us to revisit the IRX-AFUV relations, and derive these quantities directly within a self-consistent framework. We calibrate this relation for different bins of NUV-r colour and provide simple relations to relate these parameters. We investigated the robustness of our method and we conclude that the derived parameters are reliable within the uncertainties which are inherent to the adopted SED model. This calls for a deeper investigation on how well extinction and attenuation can be determined through panchromatic SED modelling.
We present ALMA detections of the [CII] 158 micron emission line and the underlying far-infrared continuum of three quasars at 6.6<z<6.9 selected from the VIKING survey. The [CII] line fluxes range between 1.6-3.4 Jy km/s ([CII] luminosities ~(1.9-3.9)x10^9 L_sun). We measure continuum flux densities of 0.56-3.29 mJy around 158 micron (rest-frame), with implied far-infrared luminosities between (0.6-7.5)x10^12 L_sun and dust masses M_d=(0.7-24)x10^8 M_sun. In one quasar we derive a dust temperature of 30^+12_-9 K from the continuum slope, below the canonical value of 47 K. Assuming that the [CII] and continuum emission are powered by star formation, we find star-formation rates from 100-1600 M_sun/yr based on local scaling relations. The L_[CII]/L_FIR ratios in the quasar hosts span a wide range from (0.3-4.6)x10^-3, including one quasar with a ratio that is consistent with local star-forming galaxies. We find that the strength of the L_[CII] and 158 micron continuum emission in z>~6 quasar hosts correlate with the quasar's bolometric luminosity. In one quasar, the [CII] line is significantly redshifted by ~1700 km/s with respect to the MgII broad emission line. Comparing to values in the literature, we find that, on average, the MgII is blueshifted by 480 km/s (with a standard deviation of 630 km/s) with respect to the host galaxy redshift, i.e. one of our quasars is an extreme outlier. Through modeling we can rule out a flat rotation curve for our brightest [CII] emitter. Finally, we find that the ratio of black hole mass to host galaxy (dynamical) mass is higher by a factor 3-4 (with significant scatter) than local relations.
In our first paper, we performed a detailed (i.e. bulge, disks, bars, spiral arms, rings, halo, nucleus, etc.) decomposition of 66 galaxies, with directly measured black hole masses, $M_{BH}$, that had been imaged at $3.6~\mu m$ with Spitzer. Our sample is the largest to date and, for the first time, the decompositions were checked for consistency with the galaxy kinematics. We present correlations between $M_{ BH}$ and the host spheroid (and galaxy) luminosity, $L_{sph}$ (and $L_{gal}$), and also stellar mass, $M_{*,sph}$. While most previous studies have used galaxy samples that were overwhelmingly dominated by high-mass, early-type galaxies, our sample includes 17 spiral galaxies, half of which have $M_{BH} < 10^7~M_\odot$, and allows us to better investigate the poorly studied low-mass end of the $M_{BH} - M_{*,sph}$ correlation. The bulges of early-type galaxies follow $M_{BH} \propto M_{*,sph}^{1.04 \pm 0.10}$ and define a tight red sequence with intrinsic scatter $\epsilon = 0.43 \pm 0.06~dex$ and a median $M_{BH}/M_{*,sph}$ ratio of $0.68 \pm 0.04\%$, i.e.~a $\pm 2\sigma$ range of 0.1-5%. At the low-mass end, the bulges of late-type galaxies define a much steeper blue sequence, with $M_{BH} \propto M_{*,sph}^{2-3}$, indicating that gas-rich processes feed the black hole more efficiently than the host bulge as they coevolve. We additionally report that: i) our Sersic galaxy sample follows a less steep sequence than previously reported; ii) bulges with Sersic index $n<2$, argued by some to be pseudo-bulges, are not offset to lower $M_{BH}$ from the correlation defined by the current bulge sample with $n>2$; and iii) $L_{sph}$ and $L_{gal}$ correlate equally well with $M_{BH}$, in terms of intrinsic scatter, only for early-type galaxies - once reasonable numbers of spiral galaxies are included, the correlation with $L_{ sph}$ is better than that with $L_{gal}$.
The Galactic bulge of the Milky Way is made up of stars with a broad range of metallicity, -3.0 < [Fe/H] < 1 dex. The mean of the Metallicity Distribution Function (MDF) decreases as a function of height z from the plane and, more weakly, with galactic radius. The most metal rich stars in the inner Galaxy are concentrated to the plane and the more metal poor stars are found predominantly further from the plane, with an overall vertical gradient in the mean of the MDF of about -0.45 dex/kpc. This vertical gradient is believed to reflect the changing contribution with height of different populations in the inner-most region of the Galaxy. The more metal rich stars of the bulge are part of the boxy/peanut structure and comprise stars in orbits which trace out the underlying X-shape. There is still a lack of consensus on the origin of the metal poor stars ([Fe/H] < -0.5) in the region of the bulge. Some studies attribute the more metal poor stars of the bulge to the thick disk and stellar halo that are present in the inner region, and other studies propose that the metal poor stars are a distinct "old spheroid" bulge population. Understanding the origin of the populations that make up the MDF of the bulge, and identifying if there is a unique bulge population which has formed separately from the disk and halo, has important consequences for identifying the relevant processes in the the formation and evolution of the Milky Way.
Several recent studies have performed galaxy decompositions to investigate correlations between the black hole mass and various properties of the host spheroid, but they have not converged on the same conclusions. This is because their models for the same galaxy were often significantly different and not consistent with each other in terms of fitted components. Using $3.6 \rm ~\mu m$ $Spitzer$ imagery, which is a superb tracer of the stellar mass (superior to the $K$-band), we have performed state-of-the-art multicomponent decompositions for 66 galaxies with directly measured black hole masses. Our sample is the largest to date and, unlike previous studies, contains a large number (17) of spiral galaxies with low black hole masses. We paid careful attention to the image mosaicking, sky subtraction and masking of contaminating sources. After a scrupulous inspection of the galaxy photometry (through isophotal analysis and unsharp masking) and - for the first time - 2D kinematics, we were able to account for spheroids, large-scale, intermediate-scale and nuclear disks, bars, rings, spiral arms, halos, extended or unresolved nuclear sources and partially depleted cores. For each individual galaxy, we compared our best-fit model with previous studies, explained the discrepancies and identified the optimal decomposition. Moreover, we have independently performed 1D and 2D decompositions, and concluded that, at least when modelling large, nearby galaxies, 1D techniques have more advantages than 2D techniques. Finally, we developed a prescription to estimate the uncertainties on the 1D best-fit parameters for the 66 spheroids that takes into account systematic errors, unlike popular 2D codes that only consider statistical errors.
This is the first of a series of papers on the Infrared Database of Extragalactic Observables from Spitzer (IDEOS). In this work we describe the identification of optical counterparts of the infrared sources detected in Spitzer Infrared Spectrograph (IRS) observations, and the acquisition and validation of redshifts. The IDEOS sample includes all the spectra from the Cornell Atlas of Spitzer/IRS Sources (CASSIS) of galaxies beyond the Local Group. Optical counterparts were identified from correlation of the extraction coordinates with the NASA Extragalactic Database (NED). To confirm the optical association and validate NED redshifts, we measure redshifts with unprecedented accuracy on the IRS spectra ({\sigma}(dz/(1+z))=0.0011) by using an improved version of the maximum combined pseudo-likelihood method (MCPL). We perform a multi-stage verification of redshifts that considers alternate NED redshifts, the MCPL redshift, and visual inspection of the IRS spectrum. The statistics is as follows: the IDEOS sample contains 3361 galaxies at redshift 0<z<6.42 (mean: 0.48, median: 0.14). We confirm the default NED redshift for 2429 sources and identify 124 with incorrect NED redshifts. We obtain IRS-based redshifts for 568 IDEOS sources without optical spectroscopic redshifts, including 228 with no previous redshift measurements. We provide the entire IDEOS redshift catalog in machine-readable formats. The catalog condenses our compilation and verification effort, and includes our final evaluation on the most likely redshift for each source, its origin, and reliability estimates.
We combine Spitzer and Herschel data of the star-forming region N11 in the Large Magellanic Cloud to produce detailed maps of the dust properties in the complex and study their variations with the ISM conditions. We also compare APEX/LABOCA 870um observations with our model predictions in order to decompose the 870um emission into dust and non-dust (free-free emission and CO(3-2) line) contributions. We find that in N11, the 870um can be fully accounted for by these 3 components. The dust surface density map of N11 is combined with HI and CO observations to study local variations in the gas-to-dust mass ratios. Our analysis leads to values lower than those expected from the LMC low-metallicity as well as to a decrease of the gas-to-dust mass ratio with the dust surface density. We explore potential hypotheses that could explain the low observed gas-to-dust mass ratios (variations in the XCO factor, presence of CO-dark gas or of optically thick HI or variations in the dust abundance in the dense regions). We finally decompose the local SEDs using a Principal Component Analysis (i.e. with no a priori assumption on the dust composition in the complex). Our results lead to a promising decomposition of the local SEDs in various dust components (hot, warm, cold) coherent with that expected for the region. Further analysis on a larger sample of galaxies will follow in order to understand how unique this decomposition is or how it evolves from one environment to another.
We report high resolution observations of the $^{12}$CO$(1\rightarrow0)$ and $^{13}$CO$(1\rightarrow0)$ molecular lines in the Carina Nebula and the Gum 31 region obtained with the 22-m Mopra telescope as part of the The Mopra Southern Galactic Plane CO Survey. We cover 8 deg$^2$ from $l = 285^{\circ}$ to 290$^{\circ}$, and from $b = -1.5^{\circ}$ to +0.5$^{\circ}$. The molecular gas column density distributions from both tracers have a similar range of values. By fitting a grey-body function to the observed infrared spectral energy distribution from Herschel maps, we derive gas column densities and dust temperatures. The gas column density has values in the range from $6.3\times\ 10^{20}$ to $1.4\times 10^{23}$ cm$^{-2}$, while the dust temperature has values in the range from 17 to 43 K. The gas column density derived from the dust emission is approximately described by a log-normal function for a limited range of column densities. A high-column density tail is clearly evident for the gas column density distribution, which appears to be a common feature in regions with active star formation. There are regional variations in the fraction of the mass recovered by the CO emission lines with respect to the total mass traced by the dust emission. These variations may be related to changes in the radiation field strength, variation of the atomic to molecular gas fraction across the observed region, differences in the CO molecule abundance with respect to H$_{2}$, and evolutionary stage differences of the molecular clouds that compose the Carina Nebula-Gum 31 complex.
We present a suite of extragalactic explorations of the origins and nature of globular clusters (GCs) and ultra-compact dwarfs (UCDs), and the connections between them. An example of GC metallicity bimodality is shown to reflect underlying, distinct metal-poor and metal-rich stellar halo populations. Metallicity-matching methods are used to trace the birth sites and epochs of GCs in giant E/S0s, pointing to clumpy disk galaxies at z ~ 3 for the metal-rich GCs, and to a combination of accreted and in-situ formation modes at z ~ 5-6 for the metal-poor GCs. An increasingly diverse zoo of compact stellar systems is being discovered, including objects that bridge the gaps between UCDs and faint fuzzies, and between UCDs and compact ellipticals. Many of these have properties pointing to origins as the stripped nuclei of larger galaxies, and a smoking-gun example is presented of an omega Cen-like star cluster embedded in a tidal stream.
The SCUSS is a deep $u$-band imaging survey in the south Galactic cap using the 2.3m Bok telescope. The survey observations were completed in the end of 2013, covering an area of about 5000 square degrees. We release the data in the region with an area of about 4000 deg$^2$ that is mostly covered by the Sloan digital sky survey. The data products contain calibrated single-epoch images, stacked images, photometric catalogs, and a catalog of star proper motions derived by Peng et al, 2015. The median seeing and magnitude limit ($5\sigma$) are about 2".0 and 23.2 mag, respectively. There are about 8 million objects having measurements of absolute proper motions. All the data and related documentations can be accessed through the SCUSS data release website of \url{this http URL}.
NGC4460 is an isolated lenticular galaxy, in which galactic wind has been earlier discovered as a gas outflow associated with circumnuclear regions of star formation. Using the results of observations in the Halpha line with the scanning Fabry-Perot interferometer on the SAO RAS 6-m telescope, we studied the kinematics of the ionized gas in this galaxy. The parameters of gas outflow from the plane of the galactic disk were refined within a simple geometric model. We show that it is impossible to characterize the wind by a fixed velocity value. Characteristic outflow velocities are within 30..80 km/s , and they are insufficient to make the swept-out matter ultimately leave the galaxy.
The velocity structure imprinted in the Halpha emission line profiles contains valuable information about galactic outflows. Using a set of high-resolution zoom-in cosmological simulations of galaxies at z=2, we generate Halpha emission line profiles, taking into account the temperature-dependent Halpha emissivity, as well as dust extinction. The lines can be described as a sum of two gaussians, as typically done with observations. In general, its properties are in good agreement with those observed in local isolated galaxies with similar masses and star formation rates. Blueshifted outflows are very common in the sample. They extend several kpc above the galaxy discs. They are also spread over the full extent of the discs. However, at small radii, the material with high velocities tends to remain confined within a thick disc, as part of galactic fountains or a turbulent medium, most probably due to the deeper gravitational potential at the galaxy center.
We present a freely downloadable software package for modelling the dynamics
of galaxies, which we call the Torus Mapper (TM). The package is based around
`torus mapping', which is a non-perturbative technique for creating orbital
tori for specified values of the action integrals. Given an orbital torus and a
star's position at a reference time, one can compute its position at any other
time, no matter how remote. One can also compute the velocities with which the
star will pass through any given point and the contribution it will make to the
time-averaged density there. A system of angle-action coordinates for the given
potential can be created by foliating phase space with orbital tori. Such a
foliation is facilitated by the ability of TM to create tori by interpolating
on a grid of tori.
We summarise the advantages of using TM rather than a standard time-stepper
to create orbits, and give segments of code that illustrate applications of TM
in several contexts, including setting up initial conditions for an N-body
simulation. We examine the precision of the orbital tori created by TM and the
behaviour of the code when orbits become trapped by a resonance.
Jets associated with Active Galactic Nuclei (AGN) have been observed for almost a century, initially at optical and radio wavelengths. They are now widely accepted as "exhausts" produced electromagnetically by the central, spinning, massive black hole and its orbiting, accreting gas. Observations at X-ray and, especially, gamma-ray energies have transformed our understanding of how these jets evolve dynamically, accelerate electrons (and positrons) and radiate throughout the entire electromagnetic spectrum. Some new approaches to modeling the powerful and rapidly variable TeV emission observed from many blazars are sketched. Observations at the highest TeV energies, to which the High Altitude Water Cherenkov Gamma-Ray Observatory (HAWC) will contribute, promise crucial discrimination between rival models of AGN jets.
We study non oscillating bifurcations of non homogeneous steady states of the Vlasov equation, a situation occurring in galactic models, or for Bernstein-Greene-Kruskal modes in plasma physics. We show that resonances are strongly suppressed, leading to very different phenomena with respect to the homogeneous case. Through an unstable manifold expansion, we show that the dynamics is very sensitive to the initial perturbation: the instability may saturate at small amplitude -generalizing the "trapping scaling" of plasma physics- or may grow to produce a large scale modification of the system. These analytical findings are illustrated and extended by direct numerical simulations with a cosine interaction potential.
We investigate the generation of magnetic fields from non-linear effects around recombination. As tight-coupling is gradually lost when approaching $z\simeq 1100$, the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; ii) the magnetic field is generated up to $z\simeq 10$; iii) it is in practice impossible to compute the magnetic field with a Boltzmann code for scales smaller than $1\,{\rm Mpc}$. Finally we confirm that for scales of a few ${\rm Mpc}$, this magnetic field is of order $2\times 10^{-29}{\rm G}$, many orders of magnitude smaller than what is currently observed on intergalactic scales.
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This paper presents a survey of X-ray selected active galactic nuclei (AGN) with optical spectroscopic follow-up in a $\sim 18\, \rm{deg^2}$ area of the equatorial XMM-XXL north field. A sample of 8445 point-like X-ray sources detected by XMM-Newton above a limiting flux of $F_{\rm 0.5-10\, keV} > 10^{-15} \rm\,erg\, cm^{-2}\, s^{-1}$ was matched to optical (SDSS) and infrared (WISE) counterparts. We followed up 3042 sources brighter than $r=22.5$ mag with the SDSS BOSS spectrograph. The spectra yielded a reliable redshift measurement for 2578 AGN in the redshift range $z=0.02-5.0$, with $0.5-2\rm\, keV$ luminosities ranging from $10^{39}-10^{46}\rm\,erg\,s^{-1}$. This is currently the largest published spectroscopic sample of X-ray selected AGN in a contiguous area. The BOSS spectra of AGN candidates show a bimodal distribution of optical line widths allowing a separation between broad- and narrow-emission line AGN. The former dominate our sample (70 per cent) due to the relatively bright X-ray flux limit and the optical BOSS magnitude limit. We classify the narrow emission line objects (22 per cent of full sample) using standard BPT diagnostics: the majority have line ratios indicating the dominant source of ionization is the AGN. A small number (8 per cent of full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. We term the latter two classes "elusive'' AGN. We also compare X-ray, optical and infrared color AGN selections in this field. X-ray observations reveal, the largest number of AGN. The overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. We show using spectral stacking that a large fraction of the X-ray AGN would not be selectable via optical or IR colours due to host galaxy contamination.
We present clustering analysis results from 10,540 Lyman break galaxies (LBGs) at z~4-7 that are identified in a combination of the Hubble legacy deep imaging and the complimentary large-area Subaru/Hyper Suprime-Cam data taken very recently. We measure angular correlation functions of these LBGs at z~4, 5, 6, and 7, and fit these measurements using halo occupation distribution (HOD) models that provide the estimates of halo masses, M_h~(1-20)x10^11 Msun. Our M_h estimates agree with those obtained by previous clustering studies in a UV-magnitude vs. M_h plane, and allow us to calculate stellar-to-halo mass ratios (SHMRs) of the LBGs. By comparison with the z~0 SHMR given by SDSS, we identify evolution of the SHMR from z~0 to z~4, and z~4 to z~7 at the >98% confidence levels. The SHMR decreases by a factor of ~3 from z~0 to 4, and increase by a factor of ~5 from z~4 to 7. We obtain the baryon conversion efficiency (BCE) of our LBGs at z~4, and find that the BCE increases with increasing dark matter halo mass. We finally compare our clustering+HOD estimates with the abundance matching results, and conclude that the M_h estimates of the clustering+HOD analyses agree with those of the simple abundance matching within a factor of 3, and that the agreement is better with those of the sophisticated abundance matching techniques that include subhalos, incompleteness, and/or star formation rate+stellar mass function evolution.
We report herschel observations of 100 very luminous, optically selected AGNs at z=2-3.5 with log(LUV)(erg/sec)> 46.5, where LUV=L1350A. The distribution in LUV is similar to the general distribution of SDSS AGNs in this redshift and luminosity interval. We measured SF luminosity, LSF, and SFR in 34 detected sources by fitting combined SF and WISE-based torus templates. We also obtained statistically significant stacks for the undetected sources in two luminosity groups. The sample properties are compared with those of very luminous AGNs at z>4.5. The main findings are: 1) The mean and the median SFRs of the detected sources are 1176 and 1010 Msun/yr, respectively. The mean SFR of the undetected sources is 148 Msun/yr. The ratio of SFR to BH accretion rate is approximately 80 for the detected sources and less than 10 for the undetected sources. There is no difference in LAGN and only a very small difference in L(torus) between detected and undetected sources. 2) The redshift distribution of LSF and LAGN for the most luminous, redshift 2-7 AGNs are different. The highest LAGN are found at z=~3. However, LSF of such sources peaks at z=~5. Assuming the objects in our sample are hosted by the most massive galaxies at those redshifts, we find many of them are below the main-sequence of SF galaxies at z=2-3.5. 3) The SEDs of dusty tori at high redshift are similar to those found in low redshift, low luminosity AGNs. Herschel upper limits put strong constraints on the long wavelength SED ruling out several earlier suggested torus templates. 4) We find no evidence for a luminosity dependence of the torus covering factor in sources with log(LAGN)=44-47.5. This conclusion is based on the highly uncertain and non-uniformally treated LAGN in many earlier studies. The median covering factors over this range are 0.68 for isotropic dust emission and 0.4 for anisotropic emission.
A fraction of brightest cluster galaxies (BCGs) shows bright emission in the UV and the blue part of the optical spectrum, which has been interpreted as evidence of recent star formation. Most of these results are based on the analysis of broadband photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 < z < 0.3, a subset from the Canadian Cluster Comparison Project (CCCP) sample. We identify plausible star formation histories of the galaxies by fitting Simple Stellar Populations (SSPs) as well as composite populations, consisting of a young stellar component superimposed on an intermediate/old stellar component, to accurately constrain their star formation histories. We detect prominent young (~200 Myr) stellar populations in 4 of the 19 galaxies. Of the four, the BCG in Abell 1835 shows remarkable A-type stellar features indicating a relatively large population of young stars, which is extremely unusual even amongst star forming BCGs. We constrain the mass contribution of these young components to the total stellar mass to be typically between 1% to 3%, but rising to 7% in Abell 1835. We find that the four of the BCGs with strong evidence for recent star formation (and only these four galaxies) are found within a projected distance of 5 kpc of their host cluster's X-ray peak, and the diffuse, X-ray gas surrounding the BCGs exhibit a ratio of the radiative cooling-to-free-fall time ($t_{c}/t_{ff}$) of < 10. These are also some of the clusters with the lowest central entropy. Our results are consistent with the predictions of the precipitation-driven star formation and AGN feedback model, in which the radiatively cooling diffuse gas is subject to local thermal instabilities once the instability parameter $t_{c}/t_{ff}$ falls below ~10, leading to the condensation and precipitation of cold gas. [Abridged]
We have observed the faintest sample of Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources to date, using the Australia Telescope Compact Array. We test the hypothesis that GPS and CSS sources are the youngest radio galaxies, place them into an evolutionary sequence along with a number of other young Active Galactic Nuclei (AGN) candidates, and search for evidence of the evolving accretion mode and its relationship to star formation. GPS/CSS sources have very small radio jets that have been recently launched from the central Supermassive Black Hole and grow in linear size as they evolve, which means that the linear size of the jets is an excellent indicator of the evolutionary stage of the AGN. We use high-resolution radio observations to determine the linear size of GPS/CSS sources, resolve their jets and observe their small-scale morphologies. We combine this with other multi-wavelength age indicators, including the spectral age, colours, optical spectra and Spectral Energy Distribution of the host galaxy, in an attempt to assemble all age indicators into a self-consistent model. We observe the most compact sources with Very Large Baseline Interferometry, which reveals their parsec-scale structures, giving us a range of source sizes and allowing us to test what fraction of GPS/CSS sources are young and evolving.
The construction of viable and physically-realistic interstellar dust models is only possible if the constraints imposed by laboratory data on interstellar dust analogue materials are respected and used within a meaningful theoretical framework. These physical dust models can then be directly compared to observations without the need for any tuning to fit the observations. Such models will generally fail to achieve the excellent fits to observations that empirical models are able to achieve. However, the physically-realistic approach will necessarily lead to a deeper insight and a fuller understanding of the nature and evolution of interstellar dust. The THEMIS modelling approach, based on (hydrogenated) amorphous carbons and amorphous silicates with metallic Fe and/or FeS nano-inclusions appears to be a promising move in this direction.
We combine Herschel/SPIRE sub-millimeter (submm) observations with existing
multi-wavelength data to investigate the characteristics of low redshift,
optically red galaxies detected in submm bands. We select a sample of galaxies
in the redshift range 0.01$\leq$z$\leq$0.2, having >5$\sigma$ detections in the
SPIRE 250 micron submm waveband. Sources are then divided into two sub-samples
of $red$ and $blue$ galaxies, based on their UV-optical colours. Galaxies in
the $red$ sample account for $\approx$4.2 per cent of the total number of
sources with stellar masses M$_{*}\gtrsim$10$^{10}$ Solar-mass. Following
visual classification of the $red$ galaxies, we find that $\gtrsim$30 per cent
of them are early-type galaxies and $\gtrsim$40 per cent are spirals. The
colour of the $red$-spiral galaxies could be the result of their highly
inclined orientation and/or a strong contribution of the old stellar
population.
It is found that irrespective of their morphological types, $red$ and $blue$
sources occupy environments with more or less similar densities (i.e., the
$\Sigma_5$ parameter). From the analysis of the spectral energy distributions
(SEDs) of galaxies in our samples based on MAGPHYS, we find that galaxies in
the $red$ sample (of any morphological type) have dust masses similar to those
in the $blue$ sample (i.e. normal spiral/star-forming systems). However, in
comparison to the $red$-spirals and in particular $blue$ systems,
$red$-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies
in the $red$-elliptical sample have much lower mean
star-formation/specific-star-formation rates in contrast to their counterparts
in the $blue$ sample. Our results support a scenario where dust in early-type
systems is likely to be of an external origin.
Angus et al.(2015) have recently faulted MOND as follows: Studying thirty disc galaxies from the DiskMass survey, they derive the profiles of velocity dispersion perpendicular to the discs as predicted by MOND, call them $\sigma_M(r)$. These are then compared with the dispersion profiles, $\sigma(r)$, measured as part of the DiskMass project. This is a (theory dependent) test of MOND, different from rotation-curve analysis. A nontrivial accomplishment of MOND -- not discussed by Angus et al. -- is that $\eta(r)\equiv\sigma_M(r)/\sigma(r)$ is well consistent with being $r$-independent (while $\sigma$ and $\sigma_M$ are strongly $r$ dependent). The fault found with MOND was that $\eta$ is systematically above 1 (with an average of about 1.4). I have suggested to Angus et al. that the fault may lie with the DiskMass dispersions, which may well be $\sim 30\%$ too low for the purpose at hand: Being based on population-integrated line profiles, they may be overweighed by younger populations, known to have much smaller dispersions, and scale heights, than the older populations, which weigh more heavily on the light distributions. I discuss independent evidence that supports this view. Now, Aniyan et al. (2015) have questioned the DiskMass $\sigma$ on the same basis. They show for the solar column in the Milky Way, that the population-integrated dispersion underestimates the proper $\sigma$ by $\sim 30\%$. If this mismatch found for the Milky Way is typical, correcting for it would bring the measured DiskMass $\sigma(r)$ to a remarkable agreement with the predicted MOND $\sigma_M(r)$. (Abridged)
Direct numerical integrations of the two-dimensional Fokker-Planck equation are carried out for compact objects orbiting a supermassive black hole (SBH) at the center of a galaxy. As in Papers I-III, the diffusion coefficients incorporate the effects of the lowest-order post-Newtonian corrections to the equations of motion. In addition, terms describing the loss of orbital energy and angular momentum due to the 5/2-order post-Newtonian terms are included. In the steady state, captures are found to occur in two regimes that are clearly differentiated in terms of energy, or semimajor axis; these two regimes are naturally characterized as "plunges" (low binding energy) and "EMRIs," or extreme-mass-ratio inspirals (high binding energy). The capture rate, and the distribution of orbital elements of the captured objects, are presented for two steady-state models based on the Milky Way: one with a relatively high density of remnants and one with a lower density. In both models, but particularly in the second, the steady-state energy distribution and the distribution of orbital elements of the captured objects are substantially different than if the Bahcall-Wolf energy distribution were assumed. The ability of classical relaxation to soften the blocking effects of the Schwarzschild barrier is quantified.These results, together with those of Papers I-III, suggest that a Fokker-Planck description can adequately represent the dynamics of collisional loss cones in the relativistic regime.
Dynamical estimates of the mass surface density at the solar radius can be made up to a height of 4 kpc using thick disk stars as tracers of the potential. We investigate why different Jeans estimators of the local surface density lead to puzzling and conflicting results. Using the Jeans equations, we compute the vertical (F_z) and radial (F_R) components of the gravitational force, as well as Gamma(z), defined as the radial derivative of V_c^2, with V_c^{2}= -RF_R. If we assume that the thick disk does not flare and that all the components of the velocity dispersion tensor of the thick disk have a uniform radial scalelength of 3.5 kpc, Gamma takes implausibly large negative values, when using the currently available kinematical data of the thick disk. This implies that the input parameters or the model assumptions must be revised. We have explored, using a simulated thick disk, the impact of the assumption that the scale lengths of the density and velocity dispersions do not depend on the vertical height z above the midplane. In the lack of any information about how these scale radii depend on z, we define a different strategy. By using a parameterized Galactic potential, we find that acceptable fits to F_z, F_R and Gamma are obtained for a flaring thick disk and a spherical dark matter halo with a local density larger than 0.0064 M_sun pc^{-3}. Disk-like dark matter distributions might be also compatible with the current data of the thick disk. A precise measurement of Gamma at the midplane could be very useful to discriminate between models.
We have begun an exciting era for gravitational wave detection, as several world-leading experiments are breaching the threshold of anticipated signal strengths. Pulsar timing arrays (PTAs) are pan-Galactic gravitational wave detectors that are already cutting into the expected strength of gravitational waves from cosmic strings and binary supermassive black holes in the nHz-$\mu$Hz gravitational wave band. These limits are leading to constraints on the evolutionary state of the Universe. Here, we provide a broad review of this field, from how pulsars are used as tools for detection, to astrophysical sources of uncertainty in the signals PTAs aim to see, to the primary current challenge areas for PTA work. This review aims to provide an up-to-date reference point for new parties interested in the field of gravitational wave detection via pulsar timing.
Recent observations indicate that a high production rate of positrons (strong 511 keV line) and a significant amount of excess GeV gamma-ray exist in our Galactic bulge. The latter issue can be explained by $\sim 40$ GeV dark matter annihilation through $b \bar{b}$ channel while the former one remains a mystery. On the other hand, recent studies reveal that a large amount of high density gas might exist near the Galactic Centre million years ago to account for the young, massive stars extending from 0.04 pc - 7 pc. In this article, I propose a new scenario and show that the 40 GeV dark matter annihilation model can also explain the required positron production rate (511 keV line) in the bulge due to the existence of the high density gas cloud near the supermassive black hole long time ago.
The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon - the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds, or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Most programme stars exhibit no statistically significant radial-velocit variation over this period and appear to be single, while four are found to be binaries with orbital periods of 300-2,000 days and normal eccentricity; the binary frequency for the sample is 17+-9%. The single stars mostly belong to the recently-identified ``low-C band'', while the binaries have higher absolute carbon abundances. We conclude that the nucleosynthetic process responsible for the strong carbon excess in these ancient stars is unrelated to their binary status; the carbon was imprinted on their natal molecular clouds in the early Galactic ISM by an even earlier, external source, strongly indicating that the CEMP-no stars are likely bona fide second-generation stars. We discuss potential production sites for carbon and its transfer across interstellar distances in the early ISM, and implications for the composition of high-redshift DLA systems. Abridged.
We show that the masses of red giant stars can be well predicted from their photospheric carbon and nitrogen abundances, in conjunction with their spectroscopic stellar labels log g, Teff, and [Fe/H]. This is qualitatively expected from mass-dependent post main sequence evolution. We here establish an empirical relation between these quantities by drawing on 1,475 red giants with asteroseismic mass estimates from Kepler that also have spectroscopic labels from APOGEE DR12. We assess the accuracy of our model, and find that it predicts stellar masses with fractional r.m.s. errors of about 14% (typically 0.2 Msun). From these masses, we derive ages with r.m.s errors of 40%. This empirical model allows us for the first time to make age determinations (in the range 1-13 Gyr) for vast numbers of giant stars across the Galaxy. We apply our model to 52,000 stars in APOGEE DR12, for which no direct mass and age information was previously available. We find that these estimates highlight the vertical age structure of the Milky Way disk, and that the relation of age with [alpha/M] and metallicity is broadly consistent with established expectations based on detailed studies of the solar neighbourhood.
The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the KEPLER and APOGEE surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using The Cannon, which can determine stellar masses to $\sim$ 0.07 dex from APOGEE DR12 spectra of red giants; these imply age estimates accurate to $\sim$ 0.2 dex (40 percent). We show that The Cannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 80,000 giants (including 20,000 red-clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center to R $\sim$ 20 kpc). We show that the age information in the spectra is not simply a corollary of the birth-material abundances [Fe/H] and [$\alpha$/Fe], and that even within a mono-abundance population of stars, there are age variations that vary sensibly with Galactic position. Such stellar age constraints across the Milky Way open up new avenues in Galactic archeology.
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This paper presents a survey of X-ray selected active galactic nuclei (AGN) with optical spectroscopic follow-up in a $\sim 18\, \rm{deg^2}$ area of the equatorial XMM-XXL north field. A sample of 8445 point-like X-ray sources detected by XMM-Newton above a limiting flux of $F_{\rm 0.5-10\, keV} > 10^{-15} \rm\,erg\, cm^{-2}\, s^{-1}$ was matched to optical (SDSS) and infrared (WISE) counterparts. We followed up 3042 sources brighter than $r=22.5$ mag with the SDSS BOSS spectrograph. The spectra yielded a reliable redshift measurement for 2578 AGN in the redshift range $z=0.02-5.0$, with $0.5-2\rm\, keV$ luminosities ranging from $10^{39}-10^{46}\rm\,erg\,s^{-1}$. This is currently the largest published spectroscopic sample of X-ray selected AGN in a contiguous area. The BOSS spectra of AGN candidates show a bimodal distribution of optical line widths allowing a separation between broad- and narrow-emission line AGN. The former dominate our sample (70 per cent) due to the relatively bright X-ray flux limit and the optical BOSS magnitude limit. We classify the narrow emission line objects (22 per cent of full sample) using standard BPT diagnostics: the majority have line ratios indicating the dominant source of ionization is the AGN. A small number (8 per cent of full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. We term the latter two classes "elusive'' AGN. We also compare X-ray, optical and infrared color AGN selections in this field. X-ray observations reveal, the largest number of AGN. The overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. We show using spectral stacking that a large fraction of the X-ray AGN would not be selectable via optical or IR colours due to host galaxy contamination.
We present clustering analysis results from 10,540 Lyman break galaxies (LBGs) at z~4-7 that are identified in a combination of the Hubble legacy deep imaging and the complimentary large-area Subaru/Hyper Suprime-Cam data taken very recently. We measure angular correlation functions of these LBGs at z~4, 5, 6, and 7, and fit these measurements using halo occupation distribution (HOD) models that provide the estimates of halo masses, M_h~(1-20)x10^11 Msun. Our M_h estimates agree with those obtained by previous clustering studies in a UV-magnitude vs. M_h plane, and allow us to calculate stellar-to-halo mass ratios (SHMRs) of the LBGs. By comparison with the z~0 SHMR given by SDSS, we identify evolution of the SHMR from z~0 to z~4, and z~4 to z~7 at the >98% confidence levels. The SHMR decreases by a factor of ~3 from z~0 to 4, and increase by a factor of ~5 from z~4 to 7. We obtain the baryon conversion efficiency (BCE) of our LBGs at z~4, and find that the BCE increases with increasing dark matter halo mass. We finally compare our clustering+HOD estimates with the abundance matching results, and conclude that the M_h estimates of the clustering+HOD analyses agree with those of the simple abundance matching within a factor of 3, and that the agreement is better with those of the sophisticated abundance matching techniques that include subhalos, incompleteness, and/or star formation rate+stellar mass function evolution.
We report herschel observations of 100 very luminous, optically selected AGNs at z=2-3.5 with log(LUV)(erg/sec)> 46.5, where LUV=L1350A. The distribution in LUV is similar to the general distribution of SDSS AGNs in this redshift and luminosity interval. We measured SF luminosity, LSF, and SFR in 34 detected sources by fitting combined SF and WISE-based torus templates. We also obtained statistically significant stacks for the undetected sources in two luminosity groups. The sample properties are compared with those of very luminous AGNs at z>4.5. The main findings are: 1) The mean and the median SFRs of the detected sources are 1176 and 1010 Msun/yr, respectively. The mean SFR of the undetected sources is 148 Msun/yr. The ratio of SFR to BH accretion rate is approximately 80 for the detected sources and less than 10 for the undetected sources. There is no difference in LAGN and only a very small difference in L(torus) between detected and undetected sources. 2) The redshift distribution of LSF and LAGN for the most luminous, redshift 2-7 AGNs are different. The highest LAGN are found at z=~3. However, LSF of such sources peaks at z=~5. Assuming the objects in our sample are hosted by the most massive galaxies at those redshifts, we find many of them are below the main-sequence of SF galaxies at z=2-3.5. 3) The SEDs of dusty tori at high redshift are similar to those found in low redshift, low luminosity AGNs. Herschel upper limits put strong constraints on the long wavelength SED ruling out several earlier suggested torus templates. 4) We find no evidence for a luminosity dependence of the torus covering factor in sources with log(LAGN)=44-47.5. This conclusion is based on the highly uncertain and non-uniformally treated LAGN in many earlier studies. The median covering factors over this range are 0.68 for isotropic dust emission and 0.4 for anisotropic emission.
A fraction of brightest cluster galaxies (BCGs) shows bright emission in the UV and the blue part of the optical spectrum, which has been interpreted as evidence of recent star formation. Most of these results are based on the analysis of broadband photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 < z < 0.3, a subset from the Canadian Cluster Comparison Project (CCCP) sample. We identify plausible star formation histories of the galaxies by fitting Simple Stellar Populations (SSPs) as well as composite populations, consisting of a young stellar component superimposed on an intermediate/old stellar component, to accurately constrain their star formation histories. We detect prominent young (~200 Myr) stellar populations in 4 of the 19 galaxies. Of the four, the BCG in Abell 1835 shows remarkable A-type stellar features indicating a relatively large population of young stars, which is extremely unusual even amongst star forming BCGs. We constrain the mass contribution of these young components to the total stellar mass to be typically between 1% to 3%, but rising to 7% in Abell 1835. We find that the four of the BCGs with strong evidence for recent star formation (and only these four galaxies) are found within a projected distance of 5 kpc of their host cluster's X-ray peak, and the diffuse, X-ray gas surrounding the BCGs exhibit a ratio of the radiative cooling-to-free-fall time ($t_{c}/t_{ff}$) of < 10. These are also some of the clusters with the lowest central entropy. Our results are consistent with the predictions of the precipitation-driven star formation and AGN feedback model, in which the radiatively cooling diffuse gas is subject to local thermal instabilities once the instability parameter $t_{c}/t_{ff}$ falls below ~10, leading to the condensation and precipitation of cold gas. [Abridged]
We have observed the faintest sample of Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources to date, using the Australia Telescope Compact Array. We test the hypothesis that GPS and CSS sources are the youngest radio galaxies, place them into an evolutionary sequence along with a number of other young Active Galactic Nuclei (AGN) candidates, and search for evidence of the evolving accretion mode and its relationship to star formation. GPS/CSS sources have very small radio jets that have been recently launched from the central Supermassive Black Hole and grow in linear size as they evolve, which means that the linear size of the jets is an excellent indicator of the evolutionary stage of the AGN. We use high-resolution radio observations to determine the linear size of GPS/CSS sources, resolve their jets and observe their small-scale morphologies. We combine this with other multi-wavelength age indicators, including the spectral age, colours, optical spectra and Spectral Energy Distribution of the host galaxy, in an attempt to assemble all age indicators into a self-consistent model. We observe the most compact sources with Very Large Baseline Interferometry, which reveals their parsec-scale structures, giving us a range of source sizes and allowing us to test what fraction of GPS/CSS sources are young and evolving.
The construction of viable and physically-realistic interstellar dust models is only possible if the constraints imposed by laboratory data on interstellar dust analogue materials are respected and used within a meaningful theoretical framework. These physical dust models can then be directly compared to observations without the need for any tuning to fit the observations. Such models will generally fail to achieve the excellent fits to observations that empirical models are able to achieve. However, the physically-realistic approach will necessarily lead to a deeper insight and a fuller understanding of the nature and evolution of interstellar dust. The THEMIS modelling approach, based on (hydrogenated) amorphous carbons and amorphous silicates with metallic Fe and/or FeS nano-inclusions appears to be a promising move in this direction.
We combine Herschel/SPIRE sub-millimeter (submm) observations with existing
multi-wavelength data to investigate the characteristics of low redshift,
optically red galaxies detected in submm bands. We select a sample of galaxies
in the redshift range 0.01$\leq$z$\leq$0.2, having >5$\sigma$ detections in the
SPIRE 250 micron submm waveband. Sources are then divided into two sub-samples
of $red$ and $blue$ galaxies, based on their UV-optical colours. Galaxies in
the $red$ sample account for $\approx$4.2 per cent of the total number of
sources with stellar masses M$_{*}\gtrsim$10$^{10}$ Solar-mass. Following
visual classification of the $red$ galaxies, we find that $\gtrsim$30 per cent
of them are early-type galaxies and $\gtrsim$40 per cent are spirals. The
colour of the $red$-spiral galaxies could be the result of their highly
inclined orientation and/or a strong contribution of the old stellar
population.
It is found that irrespective of their morphological types, $red$ and $blue$
sources occupy environments with more or less similar densities (i.e., the
$\Sigma_5$ parameter). From the analysis of the spectral energy distributions
(SEDs) of galaxies in our samples based on MAGPHYS, we find that galaxies in
the $red$ sample (of any morphological type) have dust masses similar to those
in the $blue$ sample (i.e. normal spiral/star-forming systems). However, in
comparison to the $red$-spirals and in particular $blue$ systems,
$red$-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies
in the $red$-elliptical sample have much lower mean
star-formation/specific-star-formation rates in contrast to their counterparts
in the $blue$ sample. Our results support a scenario where dust in early-type
systems is likely to be of an external origin.
Angus et al.(2015) have recently faulted MOND as follows: Studying thirty disc galaxies from the DiskMass survey, they derive the profiles of velocity dispersion perpendicular to the discs as predicted by MOND, call them $\sigma_M(r)$. These are then compared with the dispersion profiles, $\sigma(r)$, measured as part of the DiskMass project. This is a (theory dependent) test of MOND, different from rotation-curve analysis. A nontrivial accomplishment of MOND -- not discussed by Angus et al. -- is that $\eta(r)\equiv\sigma_M(r)/\sigma(r)$ is well consistent with being $r$-independent (while $\sigma$ and $\sigma_M$ are strongly $r$ dependent). The fault found with MOND was that $\eta$ is systematically above 1 (with an average of about 1.4). I have suggested to Angus et al. that the fault may lie with the DiskMass dispersions, which may well be $\sim 30\%$ too low for the purpose at hand: Being based on population-integrated line profiles, they may be overweighed by younger populations, known to have much smaller dispersions, and scale heights, than the older populations, which weigh more heavily on the light distributions. I discuss independent evidence that supports this view. Now, Aniyan et al. (2015) have questioned the DiskMass $\sigma$ on the same basis. They show for the solar column in the Milky Way, that the population-integrated dispersion underestimates the proper $\sigma$ by $\sim 30\%$. If this mismatch found for the Milky Way is typical, correcting for it would bring the measured DiskMass $\sigma(r)$ to a remarkable agreement with the predicted MOND $\sigma_M(r)$. (Abridged)
Direct numerical integrations of the two-dimensional Fokker-Planck equation are carried out for compact objects orbiting a supermassive black hole (SBH) at the center of a galaxy. As in Papers I-III, the diffusion coefficients incorporate the effects of the lowest-order post-Newtonian corrections to the equations of motion. In addition, terms describing the loss of orbital energy and angular momentum due to the 5/2-order post-Newtonian terms are included. In the steady state, captures are found to occur in two regimes that are clearly differentiated in terms of energy, or semimajor axis; these two regimes are naturally characterized as "plunges" (low binding energy) and "EMRIs," or extreme-mass-ratio inspirals (high binding energy). The capture rate, and the distribution of orbital elements of the captured objects, are presented for two steady-state models based on the Milky Way: one with a relatively high density of remnants and one with a lower density. In both models, but particularly in the second, the steady-state energy distribution and the distribution of orbital elements of the captured objects are substantially different than if the Bahcall-Wolf energy distribution were assumed. The ability of classical relaxation to soften the blocking effects of the Schwarzschild barrier is quantified.These results, together with those of Papers I-III, suggest that a Fokker-Planck description can adequately represent the dynamics of collisional loss cones in the relativistic regime.
Dynamical estimates of the mass surface density at the solar radius can be made up to a height of 4 kpc using thick disk stars as tracers of the potential. We investigate why different Jeans estimators of the local surface density lead to puzzling and conflicting results. Using the Jeans equations, we compute the vertical (F_z) and radial (F_R) components of the gravitational force, as well as Gamma(z), defined as the radial derivative of V_c^2, with V_c^{2}= -RF_R. If we assume that the thick disk does not flare and that all the components of the velocity dispersion tensor of the thick disk have a uniform radial scalelength of 3.5 kpc, Gamma takes implausibly large negative values, when using the currently available kinematical data of the thick disk. This implies that the input parameters or the model assumptions must be revised. We have explored, using a simulated thick disk, the impact of the assumption that the scale lengths of the density and velocity dispersions do not depend on the vertical height z above the midplane. In the lack of any information about how these scale radii depend on z, we define a different strategy. By using a parameterized Galactic potential, we find that acceptable fits to F_z, F_R and Gamma are obtained for a flaring thick disk and a spherical dark matter halo with a local density larger than 0.0064 M_sun pc^{-3}. Disk-like dark matter distributions might be also compatible with the current data of the thick disk. A precise measurement of Gamma at the midplane could be very useful to discriminate between models.
We have begun an exciting era for gravitational wave detection, as several world-leading experiments are breaching the threshold of anticipated signal strengths. Pulsar timing arrays (PTAs) are pan-Galactic gravitational wave detectors that are already cutting into the expected strength of gravitational waves from cosmic strings and binary supermassive black holes in the nHz-$\mu$Hz gravitational wave band. These limits are leading to constraints on the evolutionary state of the Universe. Here, we provide a broad review of this field, from how pulsars are used as tools for detection, to astrophysical sources of uncertainty in the signals PTAs aim to see, to the primary current challenge areas for PTA work. This review aims to provide an up-to-date reference point for new parties interested in the field of gravitational wave detection via pulsar timing.
Recent observations indicate that a high production rate of positrons (strong 511 keV line) and a significant amount of excess GeV gamma-ray exist in our Galactic bulge. The latter issue can be explained by $\sim 40$ GeV dark matter annihilation through $b \bar{b}$ channel while the former one remains a mystery. On the other hand, recent studies reveal that a large amount of high density gas might exist near the Galactic Centre million years ago to account for the young, massive stars extending from 0.04 pc - 7 pc. In this article, I propose a new scenario and show that the 40 GeV dark matter annihilation model can also explain the required positron production rate (511 keV line) in the bulge due to the existence of the high density gas cloud near the supermassive black hole long time ago.
The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon - the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds, or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Most programme stars exhibit no statistically significant radial-velocit variation over this period and appear to be single, while four are found to be binaries with orbital periods of 300-2,000 days and normal eccentricity; the binary frequency for the sample is 17+-9%. The single stars mostly belong to the recently-identified ``low-C band'', while the binaries have higher absolute carbon abundances. We conclude that the nucleosynthetic process responsible for the strong carbon excess in these ancient stars is unrelated to their binary status; the carbon was imprinted on their natal molecular clouds in the early Galactic ISM by an even earlier, external source, strongly indicating that the CEMP-no stars are likely bona fide second-generation stars. We discuss potential production sites for carbon and its transfer across interstellar distances in the early ISM, and implications for the composition of high-redshift DLA systems. Abridged.
We show that the masses of red giant stars can be well predicted from their photospheric carbon and nitrogen abundances, in conjunction with their spectroscopic stellar labels log g, Teff, and [Fe/H]. This is qualitatively expected from mass-dependent post main sequence evolution. We here establish an empirical relation between these quantities by drawing on 1,475 red giants with asteroseismic mass estimates from Kepler that also have spectroscopic labels from APOGEE DR12. We assess the accuracy of our model, and find that it predicts stellar masses with fractional r.m.s. errors of about 14% (typically 0.2 Msun). From these masses, we derive ages with r.m.s errors of 40%. This empirical model allows us for the first time to make age determinations (in the range 1-13 Gyr) for vast numbers of giant stars across the Galaxy. We apply our model to 52,000 stars in APOGEE DR12, for which no direct mass and age information was previously available. We find that these estimates highlight the vertical age structure of the Milky Way disk, and that the relation of age with [alpha/M] and metallicity is broadly consistent with established expectations based on detailed studies of the solar neighbourhood.
The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the KEPLER and APOGEE surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using The Cannon, which can determine stellar masses to $\sim$ 0.07 dex from APOGEE DR12 spectra of red giants; these imply age estimates accurate to $\sim$ 0.2 dex (40 percent). We show that The Cannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 80,000 giants (including 20,000 red-clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center to R $\sim$ 20 kpc). We show that the age information in the spectra is not simply a corollary of the birth-material abundances [Fe/H] and [$\alpha$/Fe], and that even within a mono-abundance population of stars, there are age variations that vary sensibly with Galactic position. Such stellar age constraints across the Milky Way open up new avenues in Galactic archeology.
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