We have observed two massive early-type galaxies with Keck/LRIS and measured radial gradients in the strengths of stellar absorption features from 4000-5500 \AA$\,$ and 8000-10,000 \AA. We present spatially resolved measurements of the dwarf-sensitive spectral indices NaI (8190 \AA) and Wing-Ford FeH (9915 \AA), as well as indices for species of H, C$_2$, CN, Mg, Ca, TiO, and Fe. Our measurements show a metallicity gradient in both objects, and Mg/Fe consistent with uniform $\alpha$-enhancement, matching widely observed trends for massive early-type galaxies. The NaI index and the CN$_1$ index at 4160 \AA$\,$ exhibit significantly steeper gradients, with a break at $r \sim 0.1 r_{\rm eff}$ ($r \sim 300$ pc). Inside this radius NaI and CN$_1$ increase sharply toward the galaxy center, relative to other indices. We interpret this trend as a rapid central rise in [Na/Fe] and [N/Fe]. In contrast, the FeH index exhibits a marginal decrease toward the galaxy center, relative to Fe. Our investigation is among the first to track FeH as a function of radius, and to demonstrate discrepant behavior between NaI and FeH. We suggest that a shallow gradient in FeH and steep, broken NaI profile reflect unique abundance patterns rather than a gradient in the stellar initial mass function.
NGC 4473 is a so--called double sigma (2$\sigma$) galaxy, i.e. a galaxy with rare, double peaks in its 2D stellar velocity dispersion. Here, we present the globular cluster (GC) kinematics in NGC 4473 out to $\sim10\,R_e$ (effective radii) using data from combined HST/ACS and Subaru/Suprime--Cam imaging and Keck/DEIMOS spectroscopy. We find that the 2$\sigma$ nature of NGC 4473 persists up to 3 $R_e$, though it becomes misaligned to the photometric major axis. We also observe a significant offset between the stellar and GC rotation amplitudes. This offset can be understood as a co--addition of counter--rotating stars producing little net stellar rotation. We identify a sharp radial transition in the GC kinematics at $\sim4\,R_e$ suggesting a well defined kinematically distinct halo. In the inner region ($<4\,R_e$), the blue GCs rotate along the photometric major axis, but in an opposite direction to the galaxy stars and red GCs. In the outer region ($>4\,R_e$), the red GCs rotate in an opposite direction compared to the inner region red GCs, along the photometric major axis, while the blue GCs rotate along an axis intermediate between the major and minor photometric axes. We also find a kinematically distinct population of very red GCs in the inner region with elevated rotation amplitude and velocity dispersion. The multiple kinematic components in NGC 4473 highlight the complex formation and evolutionary history of this 2$\sigma$ galaxy, as well as a distinct transition between the inner and outer components.
We explore the variability of quasars in the MgII and Hbeta broad emission lines and UV/optical continuum emission using the Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM). This is the largest spectroscopic study of quasar variability to date: our study includes 29 spectroscopic epochs from SDSS-RM over $6$ months, containing 357 quasars with MgII and 41 quasars with Hbeta . On longer timescales, the study is also supplemented with two-epoch data from SDSS-I/II. The SDSS-I/II data include an additional $2854$ quasars with MgII and 572 quasars with Hbeta. The MgII emission line is significantly variable ($\Delta f/f$ 10% on 100-day timescales), indicating that it is feasible to use the broad MgII line for reverberation mapping studies. The data also confirm that continuum variability increases with timescale and decreases with luminosity, and the continuum light curves are consistent with a damped random-walk model on rest-frame timescales of $\gtrsim 5$ days. We compare the emission-line and continuum variability to investigate the structure of the broad-line region. Broad-line variability shows a shallower increase with timescale compared to the continuum emission, demonstrating that the broad-line transfer function is not a $\delta$-function. Hbeta is more variable than MgII (roughly by a factor of $1.5$), suggesting different excitation mechanisms, optical depths and/or geometrical configuration for each emission line. The ensemble spectroscopic variability measurements enabled by the SDSS-RM project have important consequences for future studies of reverberation mapping and black hole mass estimation of $1<z<2$ quasars.
We present a metallicity analysis of 83 late-type giants within the central 1 pc of the Milky Way. K-band spectroscopy of these stars were obtained with the medium-spectral resolution integral-field spectrograph NIFS on Gemini North using laser-guide star adaptive optics. Using spectral template fitting with the MARCS synthetic spectral grid, we find that there is large variation in metallicity, with stars ranging from [M/H] $<$ -1.0 to above solar metallicity. About 6\% of the stars have [M/H] $<$ -0.5. This result is in contrast to previous observations, with smaller samples, that show stars at the Galactic center have approximately solar metallicity with only small variations. Our current measurement uncertainties are dominated by systematics in the model, especially at [M/H] $>$ 0, where there are stellar lines not represented in the model. However, the conclusion that there are low metallicity stars, as well as large variations in metallicity is robust. The metallicity may be an indicator of the origin of these stars. The low-metallicity population is consistent with that of globular clusters in the Milky Way, but their small fraction likely means that globular cluster infall is not the dominant mechanism for forming the Milky Way nuclear star cluster. The majority of stars are at or above solar metallicity, which suggests they were formed closer to the Galactic center or from the disk. In addition, our results indicate that it will be important for star formation history analyses using red giants at the Galactic center to consider the effect of varying metallicity.
The 11 Mpc H-alpha and Ultraviolet Galaxy (11HUGS) Survey traces the star formation activity of nearby galaxies. In addition within this volume the detection completeness of core-collapse supernovae (CCSNe) is high therefore by comparing these observed stellar births and deaths we can make a sensitive test of our understanding of how stars live and die. In this paper, we use the results of the Binary Population and Spectral Synthesis (BPASS) code to simulate the 11HUGS galaxies H-alpha and far-ultraviolet (FUV) star formation rate indicators (SFRIs) and simultaneously match the core-collapse supernova (CCSN) rate. We find that stellar population including interacting binary stars makes little difference to the total CCSN rate but increases the H-alpha and FUV fluxes for a constant number of stars being formed. In addition they significantly increase the predicted rate of type Ibc supernovae (SNe) relative to type II SNe to the level observed in the 11HUGS galaxies. We also find that instead of assuming a constant star formation history (SFH) for the galaxies our best fitting models have a star formation rate (SFR) that peaked more than 3 Myrs ago.
The infrared-to-X-ray (IRX) flux ratio traces the relative importance of dust cooling to gas cooling in astrophysical plasma such as supernova remnants (SNRs). We derive IRX ratios of SNRs in the LMC using Spitzer and Chandra SNR survey data and compare them with those of Galactic SNRs. IRX ratios of all the SNRs in the sample are found to be moderately greater than unity, indicating that dust grains are a more efficient coolant than gas although gas cooling may not be negligible. The IRX ratios of the LMC SNRs are systematically lower than those of the Galactic SNRs. As both dust cooling and gas cooling pertain to the properties of the interstellar medium, the lower IRX ratios of the LMC SNRs may reflect the characteristics of the LMC, and the lower dust-to- gas ratio (a quarter of the Galactic value) is likely to be the most significant factor. The observed IRX ratios are compared with theoretical predictions that yield IRX ratios an order of magnitude larger. This discrepancy may originate from the dearth of dust in the remnants due to either the local variation of the dust abundance in the preshock medium with respect to the canonical abundance or the dust destruction in the postshock medium. The non-equilibrium ionization cooling of hot gas, in particular for young SNRs, may also cause the discrepancy. Finally, we discuss implications for the dominant cooling mechanism of SNRs in low-metallicity galaxies.
We present observations of a 4 squared degree area toward the Gemini cloud obtained using J = 1-0 transitions of $^{12}$CO, $^{13}$CO and C$^{18}$O. No C$^{18}$O emission was detected. This region is composed of 36 core candidates of $^{13}$CO. These core candidates have a characteristic diameter of 0.25 pc, excitation temperatures of 7.9 K, line width of 0.54 km s$^{-1}$ and a mean mass of 1.4 M$_{\sun}$. They are likely to be starless core candidates, or transient structures, which probably disperse after $\sim$10$^6$ yr.
Among active galactic nuclei, BL Lac objects show extreme properties that have been interpreted as the effect of relativistic beaming on the emission from a plasma jet oriented close to the line of sight. The Doppler amplification of the jet emission makes them ideal targets for studying jet physics. In particular, low-power BL Lacs (LPBL) are very interesting because they probe the jet formation and emission processes at the lowest levels of accretion. However, they are difficult to identify since their emission is swamped by the radiation from the host galaxy in most observing bands. In this paper we propose a new LPBL selection method based on the mid-infrared emission, in addition to the traditional optical indices. We considered the radio-selected sample of Best & Heckman (2012, MNRAS, 421, 1569) and cross-matched it with the WISE all-sky survey. In a new diagnostic plane including the W2-W3 color and the Dn(4000) index, LPBL are located in a region scarcely populated by other sources. By filtering objects with small emission line equivalent width, we isolated 36 LPBL candidates up to redshift 0.15. Their radio luminosity at 1.4 GHz spans the range log L_r = 39.2-41.5 [erg/s]. Considering the completeness of our sample, we analyzed the BL Lac luminosity function (RLF), finding a dramatic paucity of LPBL with respect to the extrapolation of the RLF toward low power. This requires a break in the RLF located at log L_r~40.6 [erg/s]. The consequent peak in the BL Lacs number density is possibly the manifestation of a minimum power required to launch a relativistic jet.
We are presenting here a study of the cold dust in the ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, that was probably triggered by the expansion of the ionization front. We use 870 microns data obtained with LABOCA to map the dust emission. The obtained LABOCA image was compared to archival IR,radio continuum, and optical images. The 870 microns emission follows the 8 microns (Spitzer), 250 microns, and 500 microns (Herschel) emission distributions showing the classical morphology of a spherical shell. We use the 870 microns and 250 microns images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 microns emission shows that only 37% of them lie in or above the high-mass star formation threshold, most of them having candidate YSOs projected inside. A comparison of the dynamical age of the HII region with the fragmentation time, allowed us to conclude that the collect and collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may also be acting.
We present an update of the CLUMPY code for the calculation of the astrophysical J-factors (from dark matter annihilation/decay) for any Galactic or extragalactic dark matter halo including substructures: the concentration-mass relationship may now be drawn from a distribution, boost factors can include several levels of substructures, and triaxiality is a new option for dark matter haloes. This new version takes advantage of the cfitsio and HEALPix libraries to propose FITS output maps using the HEALPix pixelisation scheme. Skymaps for $\gamma$-ray and neutrino signals from generic annihilation/decay spectra are now direct outputs of CLUMPY. Smoothing by a user-defined instrumental Gaussian beam is also possible. In addition to these improvements, the main novelty is the implementation of a Jeans analysis module, to obtain dark matter density profiles from kinematic data in relaxed spherical systems (e.g., dwarf spheroidal galaxies). The code is also interfaced with the GreAT toolkit designed for Markov Chain Monte Carlo analyses, from which probability density functions and credible intervals can be obtained for velocity dispersions, dark matter profiles, and J- factors.
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Cold gas entering the central $1$ to $10^2$ pc of a galaxy fragments and condenses into clouds. The stability of the clouds determines whether they will be turned into stars or can be delivered to the central supermassive black hole (SMBH) to turn on an active galactic nucleus (AGN). The conventional criteria to assess the stability of these clouds, such as the Jeans criterion and Roche (or tidal) limit, are insufficient here, because they assume the dominance of self-gravity in binding a cloud, and neglect external agents, such as pressure and tidal forces, which are common in galactic nuclei. We formulate a new scheme for judging this stability. We first revisit the conventional Virial theorem, taking into account an external pressure, to identify the correct range of masses that lead to stable clouds. We then extend the theorem to include an external tidal field, crucial for the stability in the region of interest -- in dense star clusters, around SMBHs. We apply our extended Virial theorem to find the correct solutions to practical problems that until now were controversial, namely, the stability of the gas clumps in AGN tori, the circum-nuclear disk in the Galactic Center, and the central molecular zone of the Milky Way. The masses we derive for these structures are orders of magnitude smaller than the commonly-used Virial masses (equivalent to the Jeans mass). Moreover, we prove that these clumps are stable, contrary to what one would naively deduce from the Roche (tidal) limit.
Globular clusters (GCs) and Nuclear Stellar Clusters (NSCs) are typically composed by several stellar generations, characterized by different ages and chemical compositions. The youngest populations in NSCs appear to reside in disk-like structures, as observed in our Galaxy and in M31. Gas infall followed by formation of second generation (SG) stars in GCs may similarly form disk-like structures in the clusters nuclei. Here we explore this possibility and follow the long term evolution of stellar disks embedded in GCs, and study their affects on the evolution of the clusters. We study disks with different masses by means of detailed N-body simulations and explore their morphological and kinematic signatures on the GC structures. We find that as a second generation disk relaxes, the old, first generation, stellar population flattens and becomes more radially anisotropic, making the GC structure become more elliptical. The second generation stellar population is characterized by a lower velocity dispersion, and a higher rotational velocity, compared with the primordial older population. The strength of these kinematic signatures depends both on the relaxation time of the system and on the fractional mass of the second generation disk. We therefore conclude that SG populations formed in flattened configurations will give rise to two systematic trends: (1) Positive correlation between GC ellipticity and fraction of SG population (2) Positive correlation between GC relaxation time and ellipticity. Thereby GC ellipticities and rotation could be related to the formation of SG stars and their initial configuration.
We present $U_{336}V_{606}J_{125}H_{160}$ follow-up $HST$ observations of 16 $z\sim3$ candidate LyC emitters in the HS1549+1933 field. With these data, we obtain high spatial-resolution photometric redshifts of all sub-arcsecond components of the LyC candidates in order to eliminate foreground contamination and identify robust candidates for leaking LyC emission. Of the 16 candidates, we find one object with a robust LyC detection that is not due to foreground contamination. This object (MD5) resolves into two components; we refer to the LyC-emitting component as MD5b. MD5b has an observed 1500\AA\ to 900\AA\ flux-density ratio of $(F_{UV}/F_{LyC})_{obs}=4.0\pm2.0$, compatible with predictions from stellar population synthesis models. Neglecting IGM absorption, this ratio corresponds to lower limits to the relative (absolute) escape fraction of $f_{esc,rel}^{MD5b}=75\%\pm38\%$ ($f_{esc,abs}^{MD5b}=14\%\pm7\%$). The stellar population fit to MD5b indicates an age of $\lesssim50$Myr, which is in the youngest 10% of the $HST$ sample and the youngest third of typical $z\sim3$ Lyman break galaxies, and may be a contributing factor to its LyC detection. We obtain a revised, contamination-free estimate for the comoving specific ionizing emissivity at $z=2.85$, indicating (with large uncertainties) that star-forming galaxies provide roughly the same contribution as QSOs to the ionizing background at this redshift. Our results show that foreground contamination prevents ground-based LyC studies from obtaining a full understanding of LyC emission from $z\sim3$ star-forming galaxies. Future progress in direct LyC searches is contingent upon the elimination of foreground contaminants through high spatial-resolution observations, and upon acquisition of sufficiently deep LyC imaging to probe ionizing radiation in high-redshift galaxies.
We present a spectroscopic survey of 318 faint $(R\sim 27$, $L\sim0.1L_*)$, Ly{\alpha}-emission-selected galaxies (LAEs) at 2.5<z<3. A sample of 32 LAEs with rest-frame optical spectra from Keck/MOSFIRE are used to interpret the LAE spectra in the context of their systemic redshifts. We find that the Ly{\alpha} emission of LAEs is typically less spectrally extended than among samples of more luminous continuum-selected galaxies (LBGs) at similar redshifts. Using the MOSFIRE subsample, we find that the peak of the Ly{\alpha} line is shifted by +200 km/s with respect to systemic across a diverse set of galaxies including both LAEs and LBGs. We also find a small number of objects with significantly blueshifted Ly{\alpha} emission, a potential indicator of accreting gas. The Ly{\alpha}-to-H{\alpha} line ratios suggest that the LAEs have Ly{\alpha} escape fractions $f_{\rm esc,Ly{\alpha}} \approx 30$%, significantly higher than typical LBG samples. Using redshifts calibrated by our MOSFIRE sample, we construct composite LAE spectra, finding the first evidence for metal-enriched outflows in such intrinsically-faint high-redshift galaxies. These outflows have smaller continuum covering fractions $(f_c \approx 0.3)$ and velocities $(v_{\rm ave} \approx 100-200$ km/s, $v_{\rm max} \approx 500$ km/s$)$ than those associated with typical LBGs, suggesting that gas covering fraction is a likely driver of the high Ly{\alpha} and Ly-continuum escape fractions of LAEs. Our results suggest a similar scaling of outflow velocity with star formation rate as is observed at lower redshifts $(v_{\rm outflow} \sim {\rm SFR}^{0.25})$ and indicate that a substantial fraction of gas is ejected with $v > v_{esc}$.
The expected gamma-ray flux coming from dark matter annihilation in dwarf spheroidal (dSph) galaxies depends on the so-called 'J-factor', the integral of the squared dark matter density along the line-of-sight. We examine the degree to which estimates of J are sensitive to contamination (by foreground Milky Way stars and stellar streams) of the stellar-kinematic samples that are used to infer dark matter densities in 'ultrafaint' dSphs. Applying standard kinematic analyses to hundreds of mock data sets that include varying levels of contamination, we find that mis-classified contaminants can cause J-factors to be overestimated by orders of magnitude. Stellar-kinematic data sets for which we obtain such biased estimates tend 1) to include relatively large fractions of stars with ambiguous membership status, and 2) to give estimates for J that are sensitive to specific choices about how to weight and/or to exclude stars with ambiguous status. Comparing publicly-available stellar-kinematic samples for the nearby dSphs Reticulum II and Segue I, we find that only the latter displays both of these characteristics. Estimates of Segue I's J-factor should therefore be regarded with a larger degree of caution when planning and interpreting gamma-ray observations.
The Galaxy And Mass Assembly (GAMA) survey is one of the largest contemporary spectroscopic surveys of low-redshift galaxies. Covering an area of ~286 deg^2 (split among five survey regions) down to a limiting magnitude of r < 19.8 mag, we have collected spectra and reliable redshifts for 238,000 objects using the AAOmega spectrograph on the Anglo-Australian Telescope. In addition, we have assembled imaging data from a number of independent surveys in order to generate photometry spanning the wavelength range 1 nm - 1 m. Here we report on the recently completed spectroscopic survey and present a series of diagnostics to assess its final state and the quality of the redshift data. We also describe a number of survey aspects and procedures, or updates thereof, including changes to the input catalogue, redshifting and re-redshifting, and the derivation of ultraviolet, optical and near-infrared photometry. Finally, we present the second public release of GAMA data. In this release we provide input catalogue and targeting information, spectra, redshifts, ultraviolet, optical and near-infrared photometry, single-component S\'ersic fits, stellar masses, H$\alpha$-derived star formation rates, environment information, and group properties for all galaxies with r < 19.0 mag in two of our survey regions, and for all galaxies with r < 19.4 mag in a third region (72,225 objects in total). The database serving these data is available at this http URL
The most accurate measurements of magnetic fields in star-forming gas are based on the Zeeman observations analyzed by Crutcher et al. (2010). We show that their finding that the 3D magnetic field scales approximately as density$^{0.65}$ can also be obtained from analysis of the observed line-of-sight fields. We present two large-scale AMR MHD simulations of several thousand $M_\odot$ of turbulent, isothermal, self-gravitating gas, one with a strong initial magnetic field (Alfven Mach number $M_{A,0}= 1$) and one with a weak initial field ($M_{A,0}=10$). We construct samples of the 100 most massive clumps in each simulation and show that they exhibit a power-law relation between field strength and density in excellent agreement with the observed one. Our results imply that the average field in molecular clumps in the interstellar medium is $<B_{tot}> \sim 42 n_{H,4}^{0.65} \mu$G. Furthermore, the median value of the ratio of the line-of-sight field to density$^{0.65}$ in the simulations is within a factor of about (1.3, 1.7) of the observed value for the strong and weak field cases, respectively. The median value of the mass-to-flux ratio, normalized to the critical value, is 70% of the line-of-sight value. This is larger than the 50% usually cited for spherical clouds because the actual mass-to-flux ratio depends on the volume-weighted field, whereas the observed one depends on the mass-weighted field. Our results indicate that the typical molecular clump in the ISM is significantly supercritical (~ factor of 3). The results of our strong-field model are in very good quantitative agreement with the observations of Li et al. (2009), which show a strong correlation in field orientation between small and large scales. Because there is a negligible correlation in the weak-field model, we conclude that molecular clouds form from strongly magnetized (although magnetically supercritical) gas.
We present the results of a 135-arcmin$^2$ search for high-redshift galaxies lensed by clusters from the MAssive Cluster Survey. We use relatively shallow images obtained with the Hubble Space Telescope in four passbands, namely, F606W, F814W, F110W, and F140W. We identify 124 F814W dropouts as candidates for galaxies at $z \ge 6$. In order to fit the available broad-band photometry to galaxy spectral energy distribution templates, we develop a prior for the level of dust extinction at various redshifts. We also investigate the systematic biases incurred by the use of SED-fit software. The fits we obtain yield an estimate of 27 Lyman-break galaxies with photometric redshifts from $z \sim 7$ to 9. In addition, our survey has identified over 70 candidates with a significant probability of being lower-redshift ($z \sim 2$) interlopers. We conclude that even as few as four broad-band filters -- when combined with fitting the SEDs -- are capable of isolating promising objects. Such surveys are thus ideal both for investigating the bright end ($M_{1500} \le -19$) of the high-redshift UV luminosity function and for identifying candidate massive evolved galaxies at lower redshifts.
Partially depleted cores, as measured by core-Sersic model "break radii", are typically tens to a few hundred parsecs in size. Here we investigate the unusually large (cusp radius of 4.57 kpc) depleted core recently reported for Holm 15A, the brightest cluster galaxy of Abell 85. We model the 1D light profile, and also the 2D image (using GALFIT-CORSAIR, a tool for fitting the core-Sersic model in 2D). We find good agreement between the 1D and 2D analyses, with minor discrepancies attributable to intrinsic ellipticity gradients. We show that a simple Sersic profile (with a low index n and no depleted core) plus the known outer exponential "halo" provide a good description of the stellar distribution. We caution that while almost every galaxy light profile will have a radius where the negative logarithmic slope of the intensity profile equals 0.5, this alone does not imply the presence of a partially depleted core within this radius.
We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in this metallicity range. We carry out a detailed analysis of the chemical abundances of alpha, iron peak, light and heavy elements, and draw comparisons with the Milky Way halo and the ultra faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follows the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the TypeII supernovae. In addition to its value to help refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggestive of a fair proportion of s-process; we discuss the implication for the nucleosynthetic origin of the neutron capture elements.
We show that the cool gas masses of galactic discs reach a steady state that lasts many Gyr after their last major merger in cosmological hydrodynamic simulations. The mass of disc gas, M$_{\rm gas}$, depends upon a galaxy halo's spin and virial mass, but not upon stellar feedback. Halos with low spin have high star formation efficiency and lower disc gas mass. Similarly, lower stellar feedback leads to more star formation so the gas mass ends up nearly the same irregardless of stellar feedback strength. Even considering spin, the M$_{\rm gas}$ relation with halo mass, M$_{200}$ only shows a factor of 3 scatter. The M$_{\rm gas}$--M$_{200}$ relation show a break at M$_{200}$=$2\times10^{11}$ M$_\odot$ that corresponds to an observed break in the M$_{\rm gas}$--M$_\star$ relation. The constant disc mass stems from a shared halo gas density profile in all the simulated galaxies. In their outer regions, the profiles are isothermal. Where the profile rises above $n=10^{-3}$ cm$^{-3}$, the gas readily cools and the profile steepens. Inside the disc, rotation supports gas with a flatter density profile except where supernova explosions disrupt the disc. Energy injection from stellar feedback also provides pressure support to the halo gas to prevent runaway cooling flows. The resulting constant gas mass makes simpler models for galaxy formation possible, either using a "bathtub" model for star formation rates or when modeling chemical evolution.
Recently, Goodman et al. (2014) argued that the very long, very thin infrared dark cloud "Nessie" lies directly in the Galactic mid-plane and runs along the Scutum-Centaurus arm in position-position-velocity ($p-p-v$) space as traced by lower density $\rm {CO}$ and higher density ${\rm NH}_3$ gas. Nessie was presented as the first "bone" of the Milky Way, an extraordinarily long, thin, high-contrast filament that can be used to map our Galaxy's "skeleton." Here, we present evidence for additional bones in the Milky Way Galaxy, arguing that Nessie is not a curiosity but one of several filaments that could potentially trace Galactic structure. Our ten bone candidates are all long, filamentary, mid-infrared extinction features which lie parallel to, and no more than 20 pc from, the physical Galactic mid-plane. We use $\rm {CO}$, ${\rm N}_2{\rm H}^+$, $\rm {HCO}^+$, and ${\rm NH}_3$ radial velocity data to establish the three-dimensional location of the candidates in ${\it p-p-v}$ space. Of the ten candidates, six also: have a projected aspect ratio of $\geqq$50:1; run along, or extremely close to, the Scutum-Centaurus arm in p-p-v space; and exhibit no abrupt shifts in velocity. Evidence suggests that these candidates are marking the locations of significant spiral features, with the bone called filament 5 ("BC_18.88-0.09") being a close analog to Nessie in the Northern Sky. As molecular spectral-line and extinction maps cover more of the sky at increasing resolution and sensitivity, it should be possible to find more bones in future studies, ultimately to create a global-fit to the Galaxy's spiral arms by piecing together individual skeletal features.
The formation of massive stars and their arrival on the zero-age main-sequence occurs hidden behind dense clouds of gas and dust. In the giant Hii region NGC 3603, the radiation of a young cluster of OB stars has dispersed dust and gas in its vicinity. At a projected distance of 2:5 pc from the cluster, a bright mid-infrared (mid-IR) source (IRS 9A) had been identified as a massive young stellar object (MYSO), located on the side of a molecular clump (MM2) of gas facing the cluster. We investigated the physical conditions in MM2, based on APEX sub-mm observations using the SABOCA and SHFI instruments, and archival ATCA 3 mm continuum and CS spectral line data. We resolved MM2 into several compact cores, one of them closely associated with IRS 9A. These are likely infrared dark clouds as they do not show the typical hot-core emission lines and are mostly opaque against the mid-IR background. The compact cores have masses of up to several hundred times the solar mass and gas temperatures of about 50 K, without evidence of internal ionizing sources. We speculate that IRS 9A is younger than the cluster stars, but is in an evolutionary state after that of the compact cores.
The $1 ^3\Sigma_u^- \leftarrow X^3\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).
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Infrared (IR) luminosity is fundamental to understanding the cosmic star formation history and AGN evolution, since their most intense stages are often obscured by dust. Japanese infrared satellite, AKARI, provided unique data sets to probe these both at low and high redshifts. The AKARI performed an all sky survey in 6 IR bands (9, 18, 65, 90, 140, and 160$\mu$m) with 3-10 times better sensitivity than IRAS, covering the crucial far-IR wavelengths across the peak of the dust emission. Combined with a better spatial resolution, AKARI can measure the total infrared luminosity ($L_{TIR}$) of individual galaxies much more precisely, and thus, the total infrared luminosity density of the local Universe. In the AKARI NEP deep field, we construct restframe 8$\mu$m, 12$\mu$m, and total infrared (TIR) luminosity functions (LFs) at 0.15$<z<$2.2 using 4128 infrared sources. A continuous filter coverage in the mid-IR wavelength (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24$\mu$m) by the AKARI satellite allows us to estimate restframe 8$\mu$m and 12$\mu$m luminosities without using a large extrapolation based on a SED fit, which was the largest uncertainty in previous work. By combining these two results, we reveal dust-hidden cosmic star formation history and AGN evolution from $z$=0 to $z$=2.2, all probed by the AKARI satellite. The next generation space infrared telescope, SPICA, will revolutionize our view of the infrared Universe with superb sensitivity of the cooled 3m space telescope. We conclude with our survey proposal and future prospects with SPICA.
We present infrared galaxy luminosity functions (LFs) in the AKARI North Ecliptic Pole (NEP) deep field using recently-obtained, wider CFHT optical/near-IR images. AKARI has obtained deep images in the mid-infrared (IR), covering 0.6 deg$^2$ of the NEP deep field. However, our previous work was limited to the central area of 0.25 deg$^2$ due to the lack of optical coverage of the full AKARI NEP survey. To rectify the situation, we recently obtained CFHT optical and near-IR images over the entire AKARI NEP deep field. These new CFHT images are used to derive accurate photometric redshifts, allowing us to fully exploit the whole AKARI NEP deep field. AKARI's deep, continuous filter coverage in the mid-IR wavelengths (2.4, 3.2, 4.1, 7, 9, 11, 15, 18, and 24$\mu$m) exists nowhere else, due to filter gaps of other space telescopes. It allows us to estimate restframe 8$\mu$m and 12$\mu$m luminosities without using a large extrapolation based on spectral energy distribution (SED) fitting, which was the largest uncertainty in previous studies. Total infrared luminosity (TIR) is also obtained more reliably due to the superior filter coverage. The resulting restframe 8$\mu$m, 12$\mu$m, and TIR LFs at $0.15<z<2.2$ are consistent with previous works, but with reduced uncertainties, especially at the high luminosity-end, thanks to the wide field coverage. In terms of cosmic infrared luminosity density ($\Omega_{\mathrm{IR}}$), we found that the $\Omega_{\mathrm{IR}}$ evolves as $\propto (1+z)^{4.2\pm 0.4}$.
CIZA J2242.8+5301 ($z = 0.188$, nicknamed 'Sausage') is an extremely massive ($M_{200}\sim 2.0 \times 10^{15}M_\odot$ ), merging cluster with shock waves towards its outskirts, which was found to host numerous emission-line galaxies. We performed extremely deep Westerbork Synthesis Radio Telescope HI observations of the 'Sausage' cluster to investigate the effect of the merger and the shocks on the gas reservoirs fuelling present and future star formation (SF) in cluster members. By using spectral stacking, we find that the emission-line galaxies in the 'Sausage' cluster have, on average, as much HI gas as field galaxies (when accounting for the fact cluster galaxies are more massive than the field galaxies), contrary to previous studies. Since the cluster galaxies are more massive than the field spirals, they may have been able to retain their gas during the cluster merger. The large HI reservoirs are expected to be consumed within $\sim0.75-1.0$ Gyr by the vigorous SF and AGN activity and/or driven out by the out-flows we observe. We find that the star-formation rate in a large fraction of H$\alpha$ emission-line cluster galaxies correlates well with the radio broad band emission, tracing supernova remnant emission. This suggests that the cluster galaxies, all located in post-shock regions, may have been undergoing sustained SFR for at least 100 Myr. This fully supports the interpretation proposed by Stroe et al. (2015) and Sobral et al. (2015) that gas-rich cluster galaxies have been triggered to form stars by the passage of the shock.
Motivated by the recent, serendipitous discovery of the densest known galaxy, M60-UCD1, we present two initial findings from a follow-up search, using the Sloan Digital Sky Survey, Subaru/Suprime-Cam and Hubble Space Telescope imaging, and SOAR/Goodman spectroscopy. The first object discovered, M59-UCD3, has a similar size to M60-UCD1 (half-light radius of r_h ~ 20 pc) but is 40% more luminous (M_V ~ -14.6), making it the new densest-known galaxy. The second, M85-HCC1, has a size like a typical globular cluster r_h ~ 1.8 pc) but is much more luminous (M_V ~ -12.5). This hypercompact cluster is by far the densest confirmed free-floating stellar system, and is equivalent to the densest known nuclear star clusters. From spectroscopy, we find that both objects are relatively young (~9 Gyr and ~3 Gyr, respectively), with metal-abundances that resemble those of galaxy centers. Their host galaxies show clear signs of large-scale disturbances, and we conclude that these dense objects are the remnant nuclei of recently accreted galaxies. M59-UCD3 is an ideal target for follow-up with high-resolution imaging and spectroscopy to search for an overweight central supermassive black hole as was discovered in M60-UCD1. These findings also emphasize the potential value of ultra-compact dwarfs and massive globular clusters as tracers of the assembly histories of galaxies.
We present a series of hydrodynamic simulations of isolated galaxies with stellar mass of $10^{9} \, \rm{M}_{\odot}$. The models use a resolution of $750 \, \rm{M}_{\odot}$ per particle and include a treatment for the full non-equilibrium chemical evolution of ions and molecules (157 species in total), along with gas cooling rates computed self-consistently using the non-equilibrium abundances. We compare these to simulations evolved using cooling rates calculated assuming chemical (including ionisation) equilibrium, and we consider a wide range of metallicities and UV radiation fields, including a local prescription for self-shielding by gas and dust. We find higher star formation rates and stronger outflows at higher metallicity and for weaker radiation fields, as gas can more easily cool to a cold (few hundred Kelvin) star forming phase under such conditions. Contrary to variations in the metallicity and the radiation field, non-equilibrium chemistry generally has no strong effect on the total star formation rates or outflow properties. However, it is important for modelling molecular outflows. For example, the mass of H$_{2}$ outflowing with velocities $> 50 \, \rm{km} \, \rm{s}^{-1}$ is enhanced by a factor $\sim 20$ in non-equilibrium. We also compute the observable line emission from CII and CO. Both are stronger at higher metallicity, while CII and CO emission are higher for stronger and weaker radiation fields respectively. We find that CII is generally unaffected by non-equilibrium chemistry. However, emission from CO varies by a factor of $\sim 2 - 4$. This has implications for the mean $X_{\rm{CO}}$ conversion factor between CO emission and H$_{2}$ column density, which we find is lowered by up to a factor $\sim 2.3$ in non-equilibrium, and for the fraction of CO-dark molecular gas.
The goal of this paper is to test whether the formation rate of star clusters is proportional to the star formation rate (SFR) in galaxies. As a first step, we present the mass functions of compact clusters younger than 10 Myr in seven star-forming galaxies of diverse masses, sizes, and morphologies: the Large and Small Magellanic Clouds, NGC 4214, NGC 4449, M83, M51, and the Antennae. These cluster mass functions (CMFs) are well represented by power laws, dN/dM~M^b, with similar exponents b=-1.92+/-0.27, but with amplitudes that differ by factors up to ~10^3, corresponding to vast differences in the sizes of the cluster populations in these galaxies. We then normalize these CMFs by the SFRs in the galaxies, derived from dust-corrected H-alpha luminosities, and find that the spread in the amplitudes collapses, with a remaining rms deviation of only sigma_(logA)= 0.2. This is close to the expected dispersion from random uncertainties in the CMFs and SFRs. Thus, the data presented here are consistent with exact proportionality between the formation rates of stars and clusters. However, the data also permit weak deviations from proportionality, at the factor of two level, within the statistical uncertainties. We find the same spread in amplitudes when we normalize the mass functions of much older clusters, with ages in the range 100 to 400 Myr, by the current SFR. This is another indication of the general similarity among the cluster populations of different galaxies.
NASA's re-purposed Kepler mission -- dubbed K2 -- has brought new scientific opportunities that were not anticipated for the original Kepler mission. One science goal that makes optimal use of K2's capabilities, in particular its 360-degree ecliptic field of view, is galactic archaeology -- the study of the evolution of the Galaxy from the fossil stellar record. The thrust of this research is to exploit high-precision, time-resolved photometry from K2 in order to detect oscillations in red giant stars. This asteroseismic information can provide estimates of stellar radius (hence distance), mass and age of vast numbers of stars across the Galaxy. Here we present the initial analysis of a subset of red giants, observed towards the North Galactic Gap, during the mission's first full science campaign. We investigate the feasibility of using K2 data for detecting oscillations in red giants that span a range in apparent magnitude and evolutionary state (hence intrinsic luminosity). We demonstrate that oscillations are detectable for essentially all cool giants within the $\log g$ range $\sim 1.9-3.2$. Our detection is complete down to $\mathit{Kp}\sim 14.5$, which results in a seismic sample with little or no detection bias. This sample is ideally suited to stellar population studies that seek to investigate potential shortcomings of contemporary Galaxy models.
We show the effects of AGN-driven outflows on the ejection of heavy elements using our cosmological simulations, where super-massive black holes originate from the first stars. In the most massive galaxy, we have identified two strong outflows unambiguously driven by AGN feedback. These outflows have a speed greater than $\sim 8000$ km\,s$^{-1}$ near the AGN, and travel out to a half Mpc with $\sim 3000$ km\,s$^{-1}$. These outflows remove the remaining gas ($\sim 3$ per cent of baryons) and significant amounts of metals ($\sim 2$ per cent of total produced metals) from the host galaxy, chemically enriching the circumgalactic medium (CGM) and the intergalactic medium (IGM). 17.6 per cent of metals from this galaxy, and 18.4 per cent of total produced metals in the simulation, end up in the CGM and IGM, respectively. The metallicities of the CGM and IGM are higher with AGN feedback, while the mass--metallicity relation of galaxies is not affected very much. We also find `selective' mass-loss where iron is more effectively ejected than oxygen because of the time-delay of Type Ia Supernovae. AGN-driven outflows play an essential role not only in quenching of star formation in massive galaxies to match with observed down-sizing phenomena, but also in a large-scale chemical enrichment in the Universe. Observational constraints of metallicities and elemental abundance ratios in outflows are important to test the modelling of AGN feedback in galaxy formation.
We obtained an ALMA Cycle 0 spectral scan of the dusty LIRG NGC 4418, spanning a total of 70.7 GHz in bands 3, 6, and 7. We use a combined local thermal equilibrium (LTE) and non-LTE (NLTE) fit of the spectrum in order to identify the molecular species and derive column densities and excitation temperatures. We derive molecular abundances and compare them with other Galactic and extragalactic sources by means of a principal component analysis. We detect 317 emission lines from a total of 45 molecular species, including 15 isotopic substitutions and six vibrationally excited variants. Our LTE/NLTE fit find kinetic temperatures from 20 to 350 K, and densities between 10$^5$ and 10$^7$ cm$^{-3}$. The spectrum is dominated by vibrationally excited HC$_3$N, HCN, and HNC, with vibrational temperatures from 300 to 450 K. We find high abundances of HC$_3$N, SiO, H$_2$S, and c-HCCCH and a low CH$_3$OH abundance. A principal component analysis shows that NGC 4418 and Arp 220 share very similar molecular abundances and excitation, which clearly set them apart from other Galactic and extragalactic environments. The similar molecular abundances observed towards NCG 4418 and Arp 220 are consistent with a hot gas-phase chemistry, with the relative abundances of SiO and CH$_3$OH being regulated by shocks and X-ray driven dissociation. The bright emission from vibrationally excited species confirms the presence of a compact IR source, with an effective diameter $<$5 pc and brightness temperatures $>$350 K. The molecular abundances and the vibrationally excited spectrum are consistent with a young AGN/starburst system. We suggest that NGC 4418 may be a template for a new kind of chemistry and excitation, typical of compact obscured nuclei (CON). Because of the narrow line widths and bright molecular emission, NGC 4418 is the ideal target for further studies of the chemistry in CONs.
The evolution of a supernova remnant in a cloudy medium as a function of the volume filling factor of the clouds is studied in a three-dimensional axially symmetrical model. The model includes the mixing of heavy elements (metals) ejected by the supernova and their contribution to radiative losses. The interaction of the supernova envelope with the cloudy phase of the interstellar medium leads to nonsimultaneous, and on average earlier, onsets of the radiative phase in different parts of the supernova envelope. Growth in the volume filling factor $f$ leads to a decrease in the time for the transition of the envelope to the radiative phase and a decrease in the envelope's mean radius, due to the increased energy losses by the envelope in the cloudy medium. When the development of hydrodynamical instabilities in the supernova envelope is efficient, the thermal energy falls as $E_t\sim t^{-2.3}$, for the propagation of the supernova remnant through either a homogeneous or a cloudy medium. When the volume filling factor is $f\simgt 0.1$, a layer with excess kinetic energy andmomentumforms far behind the global shock front from the supernova, which traps the hot gas of the cavity in the central part of the supernova remnant. Metals ejected by the supernova are also enclosed in the central region of the remnant, where the initial (high) metallicity is essentially preserved. Thus, the interaction of the supernova envelope with the cloudy interstellar medium appreciably changes the dynamics and structure of the distribution of the gas in the remnant. This affects the observational characteristics of the remnant, in particularly, leading to substantial fluctuations of the emission measure of the gas with $T>10^5$~K and the velocity dispersion of the ionized gas.
We report on the optical spectroscopic analysis of a sample of 99 low-luminosity quasi-stellar objects (LLQSOs) at $z\leq 0.06$ base the Hamburg/ESO QSO survey (HES). The LLQSOs presented here offer the possibility of studying the faint end of the QSO population at smaller cosmological distances and, therefore, in greater detail. A small number of our LLQSO present no broad component. Two sources show double broad components, whereas six comply with the classic NLS1 requirements. As expected in NLR of broad line AGNs, the [S{\sc{ii}}]$-$based electron density values range between 100 and 1000 N$_{e}$/cm$^{3}$. Using the optical characteristics of Populations A and B, we find that 50\% of our sources with H$\beta$ broad emission are consistent with the radio-quiet sources definition. The remaining sources could be interpreted as low-luminosity radio-loud quasar. The BPT-based classification renders an AGN/Seyfert activity between 50 to 60\%. For the remaining sources, the possible star burst contribution might control the LINER and HII classification. Finally, we discuss the aperture effect as responsible for the differences found between data sets, although variability in the BLR could play a significant role as well.
We explore the structures of protoclusters and their relationship with high redshift clusters using the Millennium Simulation combined with a semi-analytic model. We find that protoclusters are very extended, with 90 per cent of their mass spread across $\sim35\,h^{-1}{\rm Mpc}$ comoving at $z=2$ ($\sim30\, \rm{arcmin}$). The `main halo', which can manifest as a high redshift cluster or group, is only a minor feature of the protocluster, containing less than 20 per cent of all protocluster galaxies at $z=2$. Furthermore, many protoclusters do not contain a main halo that is massive enough to be identified as a high redshift cluster. Protoclusters exist in a range of evolutionary states at high redshift, independent of the mass they will evolve to at $z=0$. We show that the evolutionary state of a protocluster can be approximated by the mass ratio of the first and second most massive haloes within the protocluster, and the $z=0$ mass of a protocluster can be estimated to within 0.2 dex accuracy if both the mass of the main halo and the evolutionary state is known. We also investigate the biases introduced by only observing star-forming protocluster members within small fields. The star formation rate required for line-emitting galaxies to be detected is typically high, which leads to the artificial loss of low mass galaxies from the protocluster sample. This effect is stronger for observations of the centre of the protocluster, where the quenched galaxy fraction is higher. This loss of low mass galaxies, relative to the field, distorts the size of the galaxy overdensity, which in turn can contribute to errors in predicting the $z=0$ evolved mass.
We present an absorption-line survey of optically thick gas clouds -- Lyman Limit Systems (LLSs) -- observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen NHI and associated metal-line transitions for 157 LLSs at z=1.76-4.39 restricted to 10^17.3 < NHI < 10^20.3. An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing NHI and that the majority of LLSs are highly ionized, confirming previous expectations. The Si^+/H^0 ratio spans nearly four orders-of-magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by z~3, nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (~5-10) that may have super-solar abundances. High Si^+/Fe^+ ratios suggest an alpha-enhanced medium whereas the Si^+/C^+ ratios do not exhibit the super-solar enhancement inferred previously for the Lya forest.
CONTEXT: Asymptotic giant branch (AGB) stars are in one of the latest
evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss
has a significant effect on the stellar evolution, and is a significant source
of heavy elements and dust grains for the interstellar medium. The mass-loss
rate can be well traced by carbon monoxide (CO) line emission.
AIMS: We present new \textit{Herschel} HIFI and IRAM 30m telescope CO line
data for a sample of 53 galactic AGB stars. The lines cover a fairly large
range of excitation energy from the $J=1\to0$ line to the $J=9\to8$ line, and
even the $J=14\to13$ line in a few cases. We perform radiative transfer
modelling for 38 of these sources to estimate their mass-loss rates.
METHODS: We used a radiative transfer code based on the Monte Carlo method to
model the CO line emission. We assume spherically symmetric circumstellar
envelopes that are formed by a constant mass-loss rate through a smoothly
accelerating wind.
RESULTS: We find models that are consistent across a broad range of CO lines
for most of the stars in our sample, i.e., a large number of the circumstellar
envelopes can be described with a constant mass-loss rate. We also find that an
accelerating wind is required to fit, in particular, the higher-J lines and
that a velocity law will have a significant effect on the model line
intensities. The results cover a wide range of mass-loss rates ($\sim 10^{-8}$
to $2\times 10^{-5}~\mathrm{M}_\odot~\mathrm{ yr}^{-1}$) and gas expansion
velocities (2 to $21.5$~ km s$^{-1}$), and include M-, S-, and C-type AGB
stars. Our results generally agree with those of earlier studies, although we
tend to find slightly lower mass-loss rates by about 40\%, on average. We also
present "bonus" lines detected during our CO observations.
Massive rotating single stars with an initial metal composition appropriate for the dwarf galaxy I Zw 18 ([Fe/H]=$-$1.7) are modelled during hydrogen burning for initial masses of 9-300 M$_{\odot}$ and rotational velocities of 0-900 km s$^{-1}$. Internal mixing processes in these models were calibrated based on an observed sample of OB-type stars in the Magellanic Clouds. Even moderately fast rotators, which may be abundant at this metallicity, are found to undergo efficient mixing induced by rotation resulting in quasi chemically-homogeneous evolution. These homogeneously-evolving models reach effective temperatures of up to 90 kK during core hydrogen burning. This, together with their moderate mass-loss rates, make them Transparent Wind Ultraviolet INtense stars (TWUIN star), and their expected numbers might explain the observed HeII ionizing photon flux in I Zw 18 and other low-metallicity HeII galaxies. Our slowly rotating stars above $\sim$80 M$_{\odot}$ evolve into late B- to M-type supergiants during core hydrogen burning, with visual magnitudes up to 19$^{\mathrm{m}}$ at the distance of I Zw 18. Both types of stars, TWUIN stars and luminous late-type supergiants, are only predicted at low metallicity. Massive star evolution at low metallicity is shown to differ qualitatively from that in metal-rich environments. Our grid can be used to interpret observations of local star-forming dwarf galaxies and high-redshift galaxies, as well as the metal-poor components of our Milky Way and its globular clusters.
Blazars have been suggested as possible neutrino sources long before the recent IceCube discovery of high-energy neutrinos. We re-examine this possibility within a new framework built upon the blazar simplified view and a self-consistent modelling of neutrino emission from individual sources. The former is a recently proposed paradigm that explains the diverse statistical properties of blazars adopting minimal assumptions on blazars' physical and geometrical properties. This view, tested through detailed Monte Carlo simulations, reproduces the main features of radio, X-ray, and gamma-ray blazar surveys and also the extragalactic gamma-ray background at energies > 10 GeV. Here we add a hadronic component for neutrino production and estimate the neutrino emission from BL Lacs as a class, "calibrated" by fitting the spectral energy distributions of a preselected sample of BL Lac objects and their (putative) neutrino spectra. Unlike all previous papers on this topic, the neutrino background is then derived by summing up at a given energy the fluxes of each BL Lac in the simulation, all characterised by their own redshift, synchrotron peak energy, gamma-ray flux, etc. Our main result is that BL Lacs as a class can explain the neutrino background seen by IceCube above ~ 0.5 PeV while they only contribute ~ 10% at lower energies, leaving room to some other population(s)/physical mechanism. However, one cannot also exclude the possibility that individual BL Lacs still make a contribution at the ~ 20% level to the IceCube low-energy events. Our scenario makes specific predictions testable in the next few years.
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We combined the spectroscopic information from the 3D-HST survey with the PEP/Herschel data to characterize the H\alpha dust attenuation properties of a sample of 79 normal star-forming galaxies at $0.7\leq z\leq1.5$ in the GOODS-S field. The sample was selected in the far-IR, at \lambda=100 and/or 160 \mu m, and only includes galaxies with a secure H\alpha detection (S/N>3). From the low resolution 3D-HST spectra we measured z and F(H\alpha) for the whole sample, rescaling the observed flux by a constant factor of 1.2 to remove the contamination by [NII]. The stellar masses, infrared and UV luminosities were derived from the SEDs by fitting multi-band data from GALEX near-UV to SPIRE500 \mu m. We derived the continuum extinction Estar(B-V) from both the IRX ratio and the UV-slope, and found an excellent agreement among them. Galaxies in the sample have 2.6x10^9$\leq$M*$\leq$3.5x10^11 Msun, intense infrared luminosity (L_IR>1.2x10^10 Lsun), high level of dust obscuration (0.1$\leq$Estar(B-V)$\leq$1.1) and strong H\alpha emission (typical observed fluxes Fobs(H\alpha)$\geq$4.1x10^-17 erg/s/cm2). The nebular extinction was estimated by comparing the observed SFR_H\alpha and the SFR_UV. We obtained f=Estar(B-V)/Eneb(B-V)=0.93$\pm$0.06, i.e. higher than the value measured in the local Universe. This result could be partially due to the adopted selection criteria, picking up the most obscured but also the H\alpha brightest sources. The derived dust correction produces a good agreement between H\alpha and IR+UV SFRs for objects with SFR$\gtrsim$20 Msun/yr and M*$\gtrsim$5x10^10 Msun, while sources with lower SFR and M* seem to require a smaller f-factor (i.e. higher H\alpha extinction correction). Our results then imply that for our sample the nebular and optical-UV extinctions are comparable and suggest that the f-factor is a function of both M* and SFR, according with previous studies.
We present a new integral-field spectroscopic dataset of the central part of the Orion Nebula (M 42), observed with the MUSE instrument at the ESO VLT. We reduced the data with the public MUSE pipeline. The output products are two FITS cubes with a spatial size of ~5.9'x4.9' (corresponding to ~0.76 pc x 0.63 pc) and a contiguous wavelength coverage of 4595...9366 Angstrom, spatially sampled at 0.2". We provide two versions with a sampling of 1.25 Angstrom and 0.85 Angstrom in dispersion direction. Together with variance cubes these files have a size of 75 and 110 GiB on disk. They represent one of the largest integral field mosaics to date in terms of information content. We make them available for use in the community. To validate this dataset, we compare world coordinates, reconstructed magnitudes, velocities, and absolute and relative emission line fluxes to the literature and find excellent agreement. We derive a two-dimensional map of extinction and present de-reddened flux maps of several individual emission lines and of diagnostic line ratios. We estimate physical properties of the Orion Nebula, using the emission line ratios [N II] and [S III] (for the electron temperature $T_e$) and [S II] and [Cl III] (for the electron density $N_e$), and show two-dimensional images of the velocity measured from several bright emission lines.
We present SIGAME (SImulator of GAlaxy Molecular Emission), a new numerical code designed to simulate the 12CO rotational line emission spectrum of galaxies. Using sub-grid physics recipes to post-process the outputs of smoothed particle hydrodynamics (SPH) simulations, a molecular gas phase is condensed out of the initial hot and partly ionised SPH gas and distributed in Giant Molecular Cloud (GMCs). The GMCs are subjected to far-UV radiation fields and cosmic ray ionisation rates which scale with the local star formation rate volume density, thereby ensuring that the thermal state of the gas is directly coupled to the in situ star formation conditions. Level populations as well as line radiative transport of the CO rotational lines are solved for with the 3-D radiative transfer code LIME. We have applied SIGAME to cosmological SPH simulations of three disk galaxies at z=2 with stellar masses in the range ~(0.5-2)x10^11 Msun and star formation rates ~40-140 Msun/yr, for which we predict a low-excitation gas with CO intensity peaks at the CO J=3-2 transition and total CO(3-2) luminosities within the range of observations of corresponding star-forming galaxies at z~1-2.5. Global CO-H2 conversion factors (alpha_CO) range from 1.4 to 1.6 Msun*pc^2/(K*km/s), i.e. about a third of the Galactic value. On resolved scales, the model galaxies display an increase in CO(J-(J-1))/CO(1-0) brightness temperature line ratios at J>=3, but a decrease in alpha_CO towards the central regions, in agreement with observations of nearby galaxies. Adopting a steeper GMC radial density profile or a more shallow mass spectrum leads to increased alpha_CO factors, though still below the Galactic value. The inclusion of high pressure (P_ext/k_B>10^4K/cm^3) environments descreases line ratios at high-J.
The field of Galactic Archaeology aims to understand the origins and evolution of the stellar populations in the Milky Way, as a way to understand galaxy formation and evolution in general. The GALAH (Galactic Archaeology with HERMES) Survey is an ambitious Australian-led project to explore the Galactic history of star formation, chemical evolution, minor mergers and stellar migration. GALAH is using the HERMES spectrograph, a novel, highly multiplexed, four-channel high-resolution optical spectrograph, to collect high-quality R ~ 28,000 spectra for one million stars in the Milky Way. From these data we will determine stellar parameters, radial velocities and abundances for up to 29 elements per star, and carry out a thorough chemical tagging study of the nearby Galaxy. There are clear complementarities between GALAH and other ongoing and planned Galactic Archaeology surveys, and also with ancillary stellar data collected by of major cosmological surveys. Combined, these data sets will provide a revolutionary view of the structure and history of the Milky Way.
We study the environmental dependence of the strength of polycyclic aromatic hydrocarbon (PAH) emission by AKARI observations of RX J0152.7-1357, a galaxy cluster at z=0.84. PAH emission reflects the physical conditions of galaxies and dominates 8 um luminosity (L8), which can directly be measured with the L15 band of AKARI. L8 to infrared luminosity (LIR) ratio is used as a tracer of the PAH strength. Both photometric and spectroscopic redshifts are applied to identify the cluster members. The L15-band-detected galaxies tend to reside in the outskirt of the cluster and have optically green colour, R-z'~ 1.2. We find no clear difference of the L8/LIR behaviour of galaxies in field and cluster environment. The L8/LIR of cluster galaxies decreases with specific-star-formation rate divided by that of main-sequence galaxies, and with LIR, consistent with the results for field galaxies. The relation between L8/LIR and LIR is between those at z=0 and z=2 in the literature. Our data also shows that starburst galaxies, which have lower L8/LIR than main-sequence, are located only in the outskirt of the cluster. All these findings extend previous studies, indicating that environment affects only the fraction of galaxy types and does not affect the L8/LIR behaviour of star-forming galaxies.
We analyze HST spectra and Chandra observations of a sample of 21 LINERs, at least 18 of which genuine AGN. We find a correlation between the X-rays and emission lines luminosities, extending over three orders of magnitude and with a dispersion of 0.36 dex; no differences emerge between LINERs with and without broad lines, or between radio-loud and radio-quiet sources. The presence of such a strong correlation is remarkable considering that for half of the sample the X-ray luminosity can not be corrected for local absorption. This connection is readily understood since the X-ray light is associated with the same source producing the ionizing photons at the origin of the line emission. This implies that we have a direct view of the LINERs nuclei in the X-rays: the circumnuclear, high column density structure (the torus) is absent in these sources. Such a conclusion is also supported by mid-infrared data. We suggest that this is due to the general paucity of gas and dust in their nuclear regions that causes also their low rate of accretion and low bolometric luminosity.
In four-particle scattering processes with transfer of mass, unlike mergers in which mass can only increase, mass of the most massive galaxies may be reduced. Elementary model describing such process is considered. In this way, it is supposed to explain observed phenomenon of downsizing when increasing of characteristic mass the heaviest galaxies over cosmological time replaces by its reduction.
We measure the location and energetics of a SIV BALQSO outflow. This ouflow has a velocity of 10,800 km s$^{-1}$ and a kinetic luminosity of $10^{45.7}$ erg s$^{-1}$, which is 5.2% of the Eddington luminosity of the quasar. From collisional excitation models of the observed SIV$/$SIV* absorption troughs, we measure a hydrogen number density of $n_\mathrm{\scriptscriptstyle H}=10^{4.3}$ cm$^{-3}$, which allows us to determine that the outflow is located 110 pc from the quasar. Since SIV is formed in the same ionization phase as CIV, our results can be generalized to the ubiquitous CIV BALs. Our accumulated distance measurements suggest that observed BAL outflows are located much farther away from the central source than is generally assumed (0.01-0.1 pc).
Our goal is to identify bipolar HII regions and to understand their morphology, their evolution, and the role they play in the formation of new generations of stars. We use the Spitzer and Herschel Hi-GAL surveys to identify bipolar HII regions. We search for their exciting star(s) and estimate their distances using near-IR data. Dense clumps are detected using Herschel-SPIRE data. MALT90 observations allow us to ascertain their association with the central HII region. We identify Class 0/I YSOs using their Spitzer and Herschel-PACS emissions. These methods will be applied to the entire sample of candidate bipolar HII regions. This paper focuses on two bipolar HII regions, one interesting in terms of its morphology, G319.88$+$00.79, and one in terms of its star formation, G010.32$-$00.15. Their exciting clusters are identified and their photometric distances estimated to be 2.6 kpc and 1.75 kpc, respectively. We suggest that these regions formed in dense and flat structures that contain filaments. They have a central ionized region and ionized lobes perpendicular to the parental cloud. The remains of the parental cloud appear as dense (more than 10^4 per cm^3) and cold (14-17 K) condensations. The dust in the PDR is warm (19-25 K). Dense massive clumps are present around the central ionized region. G010.32-00.14 is especially remarkable because five clumps of several hundred solar masses surround the central HII region; their peak column density is a few 10^23 per cm^2, and the mean density in their central regions reaches several 10^5 per cm^3. Four of them contain at least one massive YSO; these clumps also contain extended green objects and Class II methanol masers. This morphology suggests that the formation of a second generation of massive stars has been triggered by the central bipolar HII region. It occurs in the compressed material of the parental cloud.
We monitored the Dusty S-cluster object (DSO/G2) during its closest approach to the Galactic Center supermassive black hole in 2014 with ESO VLT/SINFONI. We report on our findings, i.e. ionized-hydrogen emission from the DSO that remains spatially compact before and after the peribothron passage. The detection of DSO/G2 object as a compact single-peak emission line source is in contradiction with the original hypothesis of a core-less cloud that is necessarily tidally stretched, hence producing double-peak emission line profile around the pericentre passage. This strengthens the evidence that the DSO/G2 source is a dust-enshrouded young star. The accretion of material from the circumstellar disc onto the stellar surface can contribute significantly to the emission of Br$\gamma$ line as well as to the observed large line width of the order of 10 angstroms.
We report the discovery of a new young stellar cluster in the outer Galaxy
located at the position of an IRAS PSC source that has been previously
mis-identified as an external galaxy. The cluster is seen in our near-infrared
imaging towards IRAS 04186+5143 and in archive Spitzer images confirming the
young stellar nature of the sources detected. There is also evidence of
sub-clustering seen in the spatial distributions of young stars and of gas and
dust.
Near- and mid-infrared photometry indicates that the stars exhibit colours
compatible with reddening by interstellar and circumstellar dust and are likely
to be low- and intermediate-mass YSOs with a large proportion of Class I YSOs.
Ammonia and CO lines were detected, with the CO emission well centred near
the position of the richest part of the cluster. The velocity of the CO and
NH$_3$ lines indicates that the gas is Galactic and located at a distance of
about 5.5 kpc, in the outer Galaxy.
Herschel data of this region characterise the dust environment of this
molecular cloud core where the young cluster is embedded. We derive masses,
luminosities and temperatures of the molecular clumps where the young stars
reside and discuss their evolutionary stages.
We present a multi-wavelength analysis of the history of star formation in the W3 complex. Using deep, near-infrared ground-based images, combined with images obtained with Spitzer and Chandra observatories, we identified and classified young embedded sources. We identified the principal clusters in the complex, and determined their structure and extension. We constructed extinction-limited samples for five principal clusters, and constructed K-band luminosity functions (KLF) that we compare with those of artificial clusters with varying ages. This analysis provided mean ages and possible age spreads for the clusters. We found that IC 1795, the centermost cluster of the complex, still hosts a large fraction of young sources with circumstellar disks. This indicates that star formation was active in IC 1795 as recently as 2 Myr ago, simultaneous to the star forming activity in the flanking embedded clusters, W3-Main and W3(OH). A comparison with carbon monoxide emission maps indicates strong velocity gradients in the gas clumps hosting W3-Main and W3(OH) and show small receding clumps of gas at IC 1795, suggestive of rapid gas removal (faster than the T Tauri timescale) in the cluster forming regions. We discuss one possible scenario for the progression of cluster formation in the W3 complex. We propose that early processes of gas collapse in the main structure of the complex could have defined the progression of cluster formation across the complex with relatively small age differences from one group to another. However, triggering effects could act as catalysts for enhanced efficiency of formation at a local level, in agreement with previous studies.
We analyse whether a stellar atmosphere model computed with the code CMFGEN provides an optimal description of the stellar observations of WR 136 and simultaneously reproduces the nebular observations of NGC 6888, such as the ionization degree, which is modelled with the pyCloudy code. All the observational material available (far and near UV and optical spectra) were used to constrain such models. We found that even when the stellar luminosity and the mass-loss rate were well constrained, the stellar temperature T_* at tau = 20, can be in a range between 70 000 and 110 000 K. When using the nebula as an additional restriction we found that the stellar models with T_* \sim 70 000 K represent the best solution for both, the star and the nebula. Results from the photoionization model show that if we consider a chemically homogeneous nebula, the observed N^+/O^+ ratios found in different nebular zones can be reproduced, therefore it is not necessary to assume a chemical inhomogeneous nebula. Our work shows the importance of calculating coherent models including stellar and nebular constraints. This allowed us to determine, in a consistent way, all the physical parameters of both the star and its associated nebula. The chemical abundances derived are 12 + log(N/H) = 9.95, 12 + log(C/H) = 7.84 and 12 + log(O/H) = 8.76 for the star and 12 + log(N/H) = 8.40, 12 + log(C/H) = 8.86 and 12 + log(O/H) = 8.20. Thus the star and the nebula are largely N- and C- enriched and O-depleted.
We present narrow-band optical and near-IR imaging and optical long-slit spectroscopic observations of Hu1-2, a Galactic planetary nebula (PN) with a pair of [N II]-bright, fast-moving (> 340 km/s) bipolar knots. Intermediate-dispersion spectra are used to derive physical conditions and abundances across the nebula, and high-dispersion spectra to study the spatio-kinematical structure. Generally Hu1-2 has high He/H (~0.14) and N/O ratios (~0.9), typical of Type I PNe. On the other hand, its abundances of O, Ne, S, and Ar are low as compared with the average abundances of Galactic bulge and disc PNe. The position-velocity maps can be generally described as an hour-glass shaped nebula with bipolar expansion, although the morphology and kinematics of the innermost regions cannot be satisfactorily explained with a simple, tilted equatorial torus. The spatio-kinematical study confines the inclination angle of its major axis to be within 10 degrees of the plane of sky. As in the irradiated bow-shocks of IC4634 and NGC7009, there is a clear stratification in the emission peaks of [O III], H_alpha, and [N II] in the northwest (NW) knot of Hu1-2. Fast collimated outflows in PNe exhibit higher excitation than other low-ionization structures. This is particularly the case for the bipolar knots of Hu1-2, with He II emission levels above those of collimated outflows in other Galactic PNe. The excitation of the knots in Hu1-2 is consistent with the combined effects of shocks and UV radiation from the central star. The mechanical energy and luminosity of the knots are similar to those observed in the PNe known to harbor a post-common envelope (post-CE) close binary central star.
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After two ALMA observing cycles, only a handful of [CII] $158\,\mu m$ emission line searches in z>6 galaxies have reported a positive detection, questioning the applicability of the local [CII]-SFR relation to high-z systems. To investigate this issue we use the Vallini et al. 2013 (V13) model, based on high-resolution, radiative transfer cosmological simulations to predict the [CII] emission from the interstellar medium of a z~7 (halo mass $M_h=1.17\times10^{11}M_{\odot}$) galaxy. We improve the V13 model by including (a) a physically-motivated metallicity (Z) distribution of the gas, (b) the contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic Microwave Background on the [CII] line luminosity. We study the relative contribution of diffuse neutral gas to the total [CII] emission ($F _{diff}/F_{tot}$) for different SFR and Z values. We find that the [CII] emission arises predominantly from PDRs: regardless of the galaxy properties, $F _{diff}/F_{tot}\leq 10$% since, at these early epochs, the CMB temperature approaches the spin temperature of the [CII] transition in the cold neutral medium ($T_{CMB}\sim T_s^{CNM}\sim 20$ K). Our model predicts a high-z [CII]-SFR relation consistent with observations of local dwarf galaxies ($0.02<Z/Z_{\odot}<0.5$). The [CII] deficit suggested by actual data ($L_{CII}<2.0\times 10^7 L_{\odot}$ in BDF3299 at z~7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local [CII]-SFR would then imply a modified Kennicutt-Schmidt relation in z>6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities ($Z<0.1 Z_{\odot}$).
At bright radio powers ($P_{\rm 1.4 GHz} > 10^{25}$ W/Hz) the space density of the most powerful sources peaks at higher redshift than that of their weaker counterparts. This paper establishes whether this luminosity-dependent evolution persists for sources an order of magnitude fainter than those previously studied, by measuring the steep--spectrum radio luminosity function (RLF) across the range $10^{24} < P_{\rm 1.4 GHz} < 10^{28}$ W/Hz, out to high redshift. A grid-based modelling method is used, in which no assumptions are made about the RLF shape and high-redshift behaviour. The inputs to the model are the same as in Rigby et al. (2011): redshift distributions from radio source samples, together with source counts and determinations of the local luminosity function. However, to improve coverage of the radio power vs. redshift plane at the lowest radio powers, a new faint radio sample is introduced. This covers 0.8 sq. deg., in the Subaru/XMM-Newton Deep Field, to a 1.4 GHz flux density limit of $S_{\rm 1.4 GHz} \geq 100~\mu$Jy, with 99% redshift completeness. The modelling results show that the previously seen high-redshift declines in space density persist to $P_{\rm 1.4 GHz} < 10^{25}$ W/Hz. At $P_{\rm 1.4 GHz} > 10^{26}$ W/Hz the redshift of the peak space density increases with luminosity, whilst at lower radio luminosities the position of the peak remains constant within the uncertainties. This `cosmic downsizing' behaviour is found to be similar to that seen at optical wavelengths for quasars, and is interpreted as representing the transition from radiatively efficient to inefficient accretion modes in the steep-spectrum population. This conclusion is supported by constructing simple models for the space density evolution of these two different radio galaxy classes; these are able to successfully reproduce the observed variation in peak redshift.
We investigate the supernova-driven galactic wind of the barred spiral galaxy NGC 7552, using both ground-based optical nebular emission lines and far-ultraviolet absorption lines measured with the Hubble Space Telescope Cosmic Origins Spectrograph. We detect broad (~300 km/s) blueshifted (-40 km/s) optical emission lines associated with the galaxy's kpc-scale star-forming ring. The broad line kinematics and diagnostic line ratios suggest that the H-alpha emission comes from clouds of high density gas entrained in a turbulent outflow. We compare the H-alpha emission line profile to the UV absorption line profile measured along a coincident sight line and find significant differences. The maximum blueshift of the H-alpha-emitting gas is ~290 km/s, whereas the UV line profile extends to blueshifts upwards of 1000 km/s. The mass outflow rate estimated from the UV is roughly nine times greater than that estimated from H-alpha. We argue that the H-alpha emission traces a cluster-scale outflow of dense, low velocity gas at the base of the large-scale wind. We suggest that UV absorption line measurements are therefore more reliable tracers of warm gas in starburst-driven outflows.
We study the sources of biases and systematics in the derivation of galaxy properties of observational studies, focusing on stellar masses, star formation rates, gas/stellar metallicities, stellar ages and magnitudes/colors. We use hydrodynamical cosmological simulations of galaxy formation, for which the real quantities are known, and apply observational techniques to derive the observables. We also make an analysis of biases that are relevant for a proper comparison between simulations and observations. For our study, we post-process the simulation outputs to calculate the galaxies' spectral energy distributions (SEDs) using Stellar Population Synthesis models and also generating the fully-consistent far UV-submillimeter wavelength SEDs with the radiative transfer code SUNRISE. We compared the direct results of simulations with the observationally-derived quantities obtained in various ways, and found that systematic differences in all studied galaxy properties appear, which are caused by: (1) purely observational biases (e.g. fiber size for single-fiber spectroscopic surveys), (2) the use of mass-weighted/luminosity-weighted quantities, with preferential sampling of more massive/luminous regions, (3) the different ways to construct the template of models when a fit to the spectra is performed, and (4) variations due to the use of different calibrations, most notably in the cases of the gas metallicities and star formation rates. Our results show that large differences, in some cases of more than an order of magnitude, can appear depending on the technique used to derive galaxy properties. Understanding these differences is of primary importance both for simulators, to allow a better judgement on similarities/differences with observations, and for observers, to allow a proper interpretation of the data which inevitably suffers from observational biases which vary from survey to survey.
We use a sample of 37 of the densest clusters and protoclusters across $1.3 \le z \le 3.2$ from the Clusters Around Radio-Loud AGN (CARLA) survey to study the formation of massive cluster galaxies. We use optical $i'$-band and infrared 3.6$\mu$m and 4.5$\mu$m images to statistically select sources within these protoclusters and measure their median observed colours; $\langle i'-[3.6] \rangle$. We find the abundance of massive galaxies within the protoclusters increases with decreasing redshift, suggesting these objects may form an evolutionary sequence, with the lower redshift clusters in the sample having similar properties to the descendants of the high redshift protoclusters. We find that the protocluster galaxies have an approximately unevolving observed-frame $i'-[3.6]$ colour across the examined redshift range. We compare the evolution of the $\langle i'-[3.6] \rangle$ colour of massive cluster galaxies with simplistic galaxy formation models. Taking the full cluster population into account, we show that the formation of stars within the majority of massive cluster galaxies occurs over at least 2Gyr, and peaks at $z \sim 2$-3. From the median $i'-[3.6]$ colours we cannot determine the star formation histories of individual galaxies, but their star formation must have been rapidly terminated to produce the observed red colours. Finally, we show that massive galaxies at $z>2$ must have assembled within 0.5Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in $z>2$ protoclusters could have formed via dry mergers.
We test the long-term kinematical stability of a Galactic stellar halo model, due to Kafle, et al. (2012), who study the kinematics of approximately 5000 blue horizontal branch (BHB) stars in the Sloan Digital Sky Survey (SDSS). The velocity dispersion $\sigma$ and anisotropy parameter $\beta$ of the stars have been determined as functions of Galactocentric radius, over the range $6<R_\mathrm{GC} < 25$ kpc, and show a strong dip in the anisotropy profile at $R_\mathrm{GC}\sim17$ kpc. By directly integrating orbits of particles in a 3-D model of the Galactic potential with these characteristics, we show that the $\sigma$ and $\beta$ profiles quickly evolve on a time scale of a $\mathrm{few}\times10$ Myr whereas the density $\rho$ profile remains largely unaffected. We suggest that the feature is therefore transient. The origin of such features in the Galactic halo remains unclear.
We present SIGAME simulations of the [CII] 157.7 {\mu}m fine structure line emission from cosmological smoothed particle hydrodynamics (SPH) simulations of main sequence galaxies at z = 2. Using sub-grid physics prescriptions the gas in our galaxy simulations is modelled as a multi-phased interstellar medium (ISM) comprised of molecular gas residing in the inner regions of giant molecular clouds, an atomic gas phase associated with photodissociation regions at the surface of the clouds, and a diffuse, fully ionized gas phase. Adopting a density profile of the clouds and taking into account heating by the local FUV radiation field and cosmic rays - both scaled by the local star formation rate density - we calculate the [CII] emission from each of the aforementioned ISM phases using a large velocity gradient approach for each cloud, on resolved and global scales. The [CII] emission peaks in the central (<~ 1 kpc) regions of our galaxies where the star formation is most intense, and we find that the majority (>~ 60%) of the emission in this region originates in the molecular gas phase. At larger galactocentric distances (>~2 kpc), the atomic gas is the main contributor to the [CII] emission (>~ 80%), and at all radii the ionized gas provides a negligible amount (<~ 5%) to the [CII] budget. Our simulations predict a log-linear relationship between the integrated [CII] luminosity and star formation rate with a slope (0.80 +/- 0.12) in agreement with observationally determined slopes (~ 0.85 - 1.00) but with a ~ 3 times higher normalization than the observed z ~ 0 relation.
Kinematical parameterisations of disc galaxies, employing emission line observations, are indispensable tools for studying the formation and evolution of galaxies. Future large-scale HI surveys will resolve the discs of many thousands of galaxies, allowing a statistical analysis of their disc and halo kinematics, mass distribution and dark matter content. Here we present an automated procedure which fits tilted-ring models to Hi data cubes of individual, well-resolved galaxies. The method builds on the 3D Tilted Ring Fitting Code (TiRiFiC) and is called FAT (Fully Automated TiRiFiC). To assess the accuracy of the code we apply it to a set of 52 artificial galaxies and 25 real galaxies from the Local Volume HI Survey (LVHIS). Using LVHIS data, we compare our 3D modelling to the 2D modelling methods DiskFit and rotcur. A conservative result is that FAT accurately models the kinematics and the morphologies of galaxies with an extent of eight beams across the major axis in the inclination range 20$^{\circ}$-90$^{\circ}$ without the need for priors such as disc inclination. When comparing to 2D methods we find that velocity fields cannot be used to determine inclinations in galaxies that are marginally resolved. We conclude that with the current code tilted-ring models can be produced in a fully automated fashion. This will be essential for future HI surveys, with the Square Kilometre Array and its pathfinders, which will allow us to model the gas kinematics of many thousands of well-resolved galaxies. Performance studies of FAT close to our conservative limits, as well as the introduction of more parameterised models will open up the possibility to study even less resolved galaxies.
We present a new calibration of the Calcium II Triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and in general it is especially suited for solar and supersolar metallicity giants, typical of external massive galaxies. About 150 bulge K giants were observed with the GIRAFFE spectrograph at VLT, both at resolution R~20,000 and at R~6,000. In the first case, the spectra allowed us to perform direct determination of Fe abundances from several unblended Fe lines, deriving what we call here high resolution [Fe/H] measurements. The low resolution spectra allowed us to measure equivalent widths of the two strongest lines of the near infrared Calcium II triplet at 8542 and 8662 A. By comparing the two measurements we derived a relation between Calcium equivalent widths and [Fe/H] that is linear over the metallicity range probed here, -1<[Fe/H]<+0.7. By adding a small second order correction, based on literature globular cluster data, we derived the unique calibration equation [Fe/H]$_{CaT} = -3.150 + 0.432W' + 0.006W'^2$, with a rms dispersion of 0.197 dex, valid across the whole metallicity range -2.3<[Fe/H]<+0.7.
The origin of high velocity stars observed in the halo of our Galaxy is still unclear. In this work we test the hypothesis, raised by results of recent high precision $N$-body simulations, of strong acceleration of stars belonging to a massive globular cluster orbitally decayed in the central region of the host galaxy where it suffers of a close interaction with a super massive black hole, which, for these test cases, we assumed $10^8$ M$_\odot$ in mass.
We present the first study of the relationship between the column density distribution of molecular clouds within nearby Galactic spiral arms and their evolutionary status as measured from their stellar content. We analyze a sample of 195 molecular clouds located at distances below 5.5 kpc, identified from the ATLASGAL 870 micron data. We define three evolutionary classes within this sample: starless clumps, star-forming clouds with associated young stellar objects, and clouds associated with HII regions. We find that the N(H2) probability density functions (N-PDFs) of these three classes of objects are clearly different: the N-PDFs of starless clumps are narrowest and close to log-normal in shape, while star-forming clouds and HII regions exhibit a power-law shape over a wide range of column densities and log-normal-like components only at low column densities. We use the N-PDFs to estimate the evolutionary time-scales of the three classes of objects based on a simple analytic model from literature. Finally, we show that the integral of the N-PDFs, the dense gas mass fraction, depends on the total mass of the regions as measured by ATLASGAL: more massive clouds contain greater relative amounts of dense gas across all evolutionary classes.
The GAMA survey has now completed its spectroscopic campaign of over 250,000 galaxies ($r<19.8$mag), and will shortly complete the assimilation of the complementary panchromatic imaging data from GALEX, VST, VISTA, WISE, and Herschel. In the coming years the GAMA fields will be observed by the Australian Square Kilometer Array Pathfinder allowing a complete study of the stellar, dust, and gas mass constituents of galaxies within the low-z Universe ($z<0.3$). The science directive is to study the distribution of mass, energy, and structure on kpc-Mpc scales over a 3billion year timeline. This is being pursued both as an empirical study in its own right, as well as providing a benchmark resource against which the outputs from numerical simulations can be compared. GAMA has three particularly compelling aspects which set it apart: completeness, selection, and panchromatic coverage. The very high redshift completeness ($\sim 98$\%) allows for extremely complete and robust pair and group catalogues; the simple selection ($r<19.8$mag) minimises the selection bias and simplifies its management; and the panchromatic coverage, 0.2$\mu$m - 1m, enables studies of the complete energy distributions for individual galaxies, well defined sub-samples, and population assembles (either directly or via stacking techniques). For further details and data releases see: this http URL
The local cosmic-ray (CR) spectra are calculated for typical characteristic regions of a cold dense molecular cloud, to investigate two so far neglected mechanisms of dust charging: collection of suprathermal CR electrons and protons by grains, and photoelectric emission from grains due to the UV radiation generated by CRs. The two mechanisms add to the conventional charging by ambient plasma, produced in the cloud by CRs. We show that the CR-induced photoemission can dramatically modify the charge distribution function for submicron grains. We demonstrate the importance of the obtained results for dust coagulation: While the charging by ambient plasma alone leads to a strong Coulomb repulsion between grains and inhibits their further coagulation, the combination with the photoemission provides optimum conditions for the growth of large dust aggregates in a certain region of the cloud, corresponding to the densities $n(\mathrm{H_2})$ between $\sim10^4$ cm$^{-3}$ and $\sim10^6$ cm$^{-3}$. The charging effect of CR is of generic nature, and therefore is expected to operate not only in dense molecular clouds but also in the upper layers and the outer parts of protoplanetary discs.
We have observed the Virgo Cluster spiral galaxy, NGC~4845, at 1.6 and 6 GHz using the Karl G. Jansky Very Large Array, as part of the `Continuum Halos in Nearby Galaxies -- an EVLA Survey' (CHANG-ES). The source consists of a bright unresolved core with a surrounding weak central disk (1.8 kpc diameter). The core is variable over the 6 month time scale of the CHANG-ES data and has increased by a factor of $\approx$ 6 since 1995. The wide bandwidths of CHANG-ES have allowed us to determine the spectral evolution of this core which peaks {\it between} 1.6 and 6 GHz (it is a GigaHertz-peaked spectrum source).We show that the spectral turnover is dominated by synchrotron self-absorption and that the spectral evolution can be explained by adiabatic expansion (outflow), likely in the form of a jet or cone. The CHANG-ES observations serendipitously overlap in time with the hard X-ray light curve obtained by Nikolajuk \& Walter (2013) which they interpret as due to a tidal disruption event (TDE) of a super-Jupiter mass object around a $10^5\, M_\odot$ black hole. We outline a standard jet model, provide an explanation for the observed circular polarization, and quantitatively suggest a link between the peak radio and peak X-ray emission via inverse Compton upscattering of the photons emitted by the relativistic electrons. We predict that it should be possible to resolve a young radio jet via VLBI as a result of this nearby TDE.
Streams of gas and dust in the inner parsec of the Galactic center form a distinct feature known as the Minispiral, which has been studied in radio waveband as well as in the infrared wavebands. A large fraction of the Minispiral gas is ionized by radiation of OB stars present in the Nuclear Star Cluster (NSC). Based on the inferred mass in the innermost parsec ($\sim 10^6$ solar masses), over $\sim 10^3$ -- $10^4$ neutron stars should move in the sphere of gravitational influence of the SMBH. We estimate that a fraction of them propagate through the denser, ionized medium concentrated mainly along the three arms of the Minispiral. Based on the properties of the gaseous medium, we discuss different interaction regimes of magnetised neutron stars passing through this region. Moreover, we sketch expected observational effects of these regimes. The simulation results may be applied to other galactic nuclei hosting NSC, where the expected distribution of the interaction regimes is different across different galaxy types.
Recent quantum mechanical calculations of rate coefficients for collisional transfer of population between the hyperfine states of 13CN enable their population densities to be determined. We have computed the relative populations of the hyperfine states of the N = 0, 1, 2 rotational states for kinetic temperatures 5 $\le$ T $\le$ 20 K and molecular hydrogen densities 1 $\le$ n(H2) $\le$10 10 cm --3. Spontaneous and induced radiative transitions were taken into account. Our calculations show that, if the lines are optically thin, the populations of the hyperfine states, F, within a given rotational manifold are proportional to their statistical weights, (2F + 1) -- i.e. in local thermodynamic equilibrium -- over the entire range of densities. We have re-analysed IRAM 30 m telescope observations of 13CN hyperfine transitions (N = 1 $\rightarrow$ 0) in four starless cores. A comparison of these observations with our calculations confirms that the hyperfine states are statistically populated in these sources.
Using the cosmological smoothed particle hydrodynamical code GADGET-3 we make a realistic assessment of the technique of using constant cumulative number density as a tracer of galaxy evolution at high redshift. We find that over a redshift range of $3\leq z \leq7$ one can on average track the growth of the stellar mass of a population of galaxies selected from the same cumulative number density bin to within $\sim 0.20$ dex. Over the stellar mass range we probe ($10^{10.39}\leq M_s/M_\odot \leq 10^{10.75}$ at $z =$ 3 and $10^{8.48}\leq M_s/M_\odot \leq 10^{9.55}$ at $z =$ 7) one can reduce this bias by selecting galaxies based on an evolving cumulative number density. We find the cumulative number density evolution exhibits a trend towards higher values which can be quantified by simple linear formulations going as $-0.10\Delta z$ for descendants and $0.12\Delta z$ for progenitors. Utilizing such an evolving cumulative number density increases the accuracy of descendant/progenitor tracking by a factor of $\sim2$. This result is in excellent agreement, within $0.10$ dex, with abundance matching results over the same redshift range. However, we find that our more realistic cosmological hydrodynamic simulations produce a much larger scatter in descendant/progenitor stellar masses than previous studies, particularly when tracking progenitors. This large scatter makes the application of either the constant cumulative number density or evolving cumulative number density technique limited to average stellar masses of populations only, as the diverse mass assembly histories caused by stochastic physical processes such as gas accretion, mergers, and star formation of individual galaxies will lead to a larger scatter in other physical properties such as metallicity and star-formation rate.
We use Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) rest-frame optical imaging to select a pilot sample of star-forming galaxies in the redshift range z = 2.00-2.65 whose multi-component morphologies are consistent with expectations for major mergers. We follow up this sample of major merger candidates with Keck/NIRSPEC longslit spectroscopy obtained in excellent seeing conditions (FWHM ~ 0.5 arcsec) to obtain Halpha-based redshifts of each of the morphological components in order to distinguish spectroscopic pairs from false pairs created by projection along the line of sight. Of six pair candidates observed, companions (estimated mass ratios 5:1 and 7:1) are detected for two galaxies down to a 3sigma limiting emission-line flux of ~ 10^{-17} erg/s/cm2. This detection rate is consistent with a ~ 50% false pair fraction at such angular separations (1-2 arcsec), and with recent claims that the star-formation rate (SFR) can differ by an order of magnitude between the components in such mergers. The two spectroscopic pairs identified have total SFR, SFR surface densities, and stellar masses consistent on average with the overall z ~ 2 star forming galaxy population.
Recent observations reveal that magnetic turbulence in the nearly colisionless solar wind plasma extends to scales smaller than the plasma microscales, such as ion gyroradius and ion inertial length. Measured breaks in the spectra of magnetic and density fluctuations at high frequencies are thought to be related to the transition from large-scale hydromagnetic to small-scale kinetic turbulence. The scales of such transitions and the responsible physical mechanisms are not well understood however. In the present work we emphasize the crucial role of the plasma parameters in the transition to kinetic turbulence, such as the ion and electron plasma beta, the electron to ion temperature ratio, the degree of obliquity of turbulent fluctuations. We then propose an explanation for the spectral breaks reported in recent observations.
Type Ia supernovae (SNe Ia) are powerful cosmological "standardizable candles" and the most precise distance indicators. However, a limiting factor in their use for precision cosmology rests on our ability to correct for the dust extinction toward them. SN 2014J in the starburst galaxy M82, the closest detected SN~Ia in three decades, provides unparalleled opportunities to study the dust extinction toward an SN Ia. In order to derive the extinction as a function of wavelength, we model the color excesses toward SN 2014J, which are observationally derived over a wide wavelength range in terms of dust models consisting of a mixture of silicate and graphite. The resulting extinction laws steeply rise toward the far ultraviolet, even steeper than that of the Small Magellanic Cloud (SMC). We infer a visual extinction of $A_V \approx 1.9~\rm mag$, a reddening of $E(B-V)\approx1.1~ \rm mag$, and a total-to-selective extinction ratio of $R_V \approx 1.7$, consistent with that previously derived from photometric, spectroscopic, and polarimetric observations. The size distributions of the dust in the interstellar medium toward SN 2014J are skewed toward substantially smaller grains than that of the Milky Way and the SMC.
The "Wide Area VISTA Extra-galactic Survey" (WAVES) is a 4MOST Consortium Design Reference Survey which will use the VISTA/4MOST facility to spectroscopically survey ~2million galaxies to $r_{\rm AB} < 22$ mag. WAVES consists of two interlocking galaxy surveys ("WAVES-Deep" and "WAVES-Wide"), providing the next two steps beyond the highly successful 1M galaxy Sloan Digital Sky Survey and the 250k Galaxy And Mass Assembly survey. WAVES will enable an unprecedented study of the distribution and evolution of mass, energy, and structures extending from 1-kpc dwarf galaxies in the local void to the morphologies of 200-Mpc filaments at $z\sim1$. A key aim of both surveys will be to compare comprehensive empirical observations of the spatial properties of galaxies, groups, and filaments, against state-of-the-art numerical simulations to distinguish between various Dark Matter models.
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