We investigate the structural properties of the underlying hosts of 34 blue compact dwarf (BCD) galaxies with deep near-infrared (NIR) photometry. The BCD sample is selected from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey in the Great observatories origins Deep Survey North and South fields. We extract the surface brightness profile (SBP) in the optical F 435W and NIR F 160W bands. The SBPs of BCDs in the H band reach 26 mag arcsec^-2 at the 3\sigma level, which is so far the deepest NIR imaging of BCDs. Then we fit the SBPs with one- and two- component Sersic models. About half of the BCDs favour the two-component model which significantly improves the fit quality. The effective radii of the underlying hosts of BCDs in the B band are smaller than those of early-type dwarfs (dEs) and dwarf irregulars at a fixed luminosity. This discrepancy is similar to findings in many previous works. However, the difference in structural parameters between BCDs and other dwarf galaxies seems to be less significant in the H band. Furthermore, we find a remarkable agreement between the underlying hosts of BCDs and dEs. All dwarf galaxies seem to follow a similar luminosity-radius relationship which suggests a unified structural evolution for dwarf galaxies. We conclude that a possible evolution track from BCDs to dEs cannot be ruled out, with no significant change of structure needed in the evolutionary scenario.
We revealed the detailed structure of a vastly extended H$\alpha$-emitting nebula ("H$\alpha$ nebula") surrounding the starburst/merging galaxy NGC 6240 by deep narrow-band imaging observations with the Subaru Suprime-Cam. The extent of the nebula is $\sim$90 kpc in diameter and the total H$\alpha$ luminosity amounts to $\approx 1.6 \times 10^{42}$ erg s$^{-1}$. The volume filling factor and the mass of the warm ionized gas are $\sim$10$^{-4}$--10$^{-5}$ and $\sim$$5 \times 10^8$ $M_\odot$, respectively. The nebula has a complicated structure, which includes numerous filaments, loops, bubbles, and knots. We found that there is a tight spatial correlation between the H$\alpha$ nebula and the extended soft X-ray-emitting gas, both in large and small scales. The overall morphology of the nebula is dominated by filamentary structures radially extending from the center of the galaxy. A large-scale bi-polar bubble extends along the minor axis of the main stellar disk. The morphology strongly suggests that the nebula was formed by intense outflows - superwinds - driven by starbursts. We also found three bright knots embedded in a looped filament of ionized gas that show head-tail morphologies in both emission-line and continuum, suggesting close interactions between the outflows and star forming regions. Based on the morphology and surface brightness distribution of the H$\alpha$ nebula, we propose the scenario that three major episodes of starburst/superwind activities which were initiated $\sim$10$^2$ Myr ago formed the extended ionized gas nebula of NGC 6240.
If the Universe is dominated by cold dark matter and dark energy as in the currently popular LCDM cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass M > ~10^14 Msun appearing at around 6 Gyrs after the Big Bang (z ~ 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few x 10^13 Msun at redshifts between z=0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited samples of galaxies using a combination of spectroscopic and photometric redshifts. We analyze the Millennium simulation data in a similar way to the analysis of the observational data in order to test the LCDM cosmology. We find that there are too many massive structures (M > 7 x 10^13 Msun) observed at z > 2 in comparison with the simulation predictions by a factor of a few, giving a probability of < 1/2500 of the observed data being consistent with the simulation. Our result suggests that massive structures have emerged early, but the reason for the discrepancy with the simulation is unclear. It could be due to the limitation of the simulation such as the lack of key, unrecognized ingredients (strong non-Gaussianity or other baryonic physics), or simply a difficulty in the halo mass estimation from observation, or a fundamental problem of the LCDM cosmology. On the other hand, the over-abundance of massive structures at high redshifts does not favor heavy neutrino mass of ~ 0.3 eV or larger, as heavy neutrinos make the discrepancy between the observation and the simulation more pronounced by a factor of 3 or more.
Low-redshift active galactic nuclei (AGNs) with extremely blue optical
spectral indices are shown to have a mean, velocity-averaged, broad-line
H$\alpha$/H$\beta$ ratio of $\thickapprox 2.72 \pm 0.04$, consistent with the
Baker-Menzel Case B value. Comparison of a wide range of properties of the very
bluest AGNs with those of a luminosity-matched subset of the Dong et al. blue
AGN sample indicates that the only difference is the internal reddening.
Ultraviolet fluxes are brighter for the bluest AGNs by an amount consistent
with the flat AGN reddening curve of Gaskell et al. (2004). The lack of a
significant difference in the GALEX (FUV--NUV) colour index strongly rules out
a steep SMC-like reddening curve and also argues against an intrinsically
harder spectrum. For very blue AGNs the Ly$\alpha$/H$\beta$ ratio is also
consistent with being the Case B value. The Case B ratios provide strong
support for the self-shielded broad-line model of Gaskell, Klimek & Nazarova.
It is proposed that the greatly enhanced Ly$\alpha$/H$\beta$ ratio at very high
velocities is a consequence of continuum fluorescence in the Lyman lines (Case
C).
Reddenings of AGNs mean that the far-UV luminosity is underestimated by an
order of magnitude. This will be the main cause of the discrepancies between
measured accretion disc sizes and the predictions of simple accretion disc
theory. The greater luminosity of AGNs also resolves the photon underproduction
problem for the intergalactic medium. The total mass in lower mass supermassive
black holes must be greater than hitherto estimated.
We present the results of initial spectrographic followup with the Very Large Telescope (UT3, Melipal) for $K_s \ge 14$ Galactic plane CIV emission-line candidates in the near-infrared (NIR). These 7 faint stars all display prominent HeI and CIV emission lines characteristic of a carbon-rich Wolf-Rayet star. They have NIR colours which are much too blue to be those of distant, classical WR stars. The magnitudes and colours are compatible with those expected for central stars of planetary nebulae, and are likely to come from massive progenitor populations, and themselves be more massive than any sample of planetary nebulae known. Our survey has identified thousands of such candidates.
Links to: arXiv, form interface, find, astro-ph, recent, 1601, contact, help (Access key information)
Measurement of the evolution of both active galactic nuclei (AGN) and star-formation in galaxies underpins our understanding of galaxy evolution over cosmic time. Radio continuum observations can provide key information on these two processes, in particular via the mechanical feedback produced by radio jets in AGN, and via an unbiased dust-independent measurement of star-formation rates. In this paper we determine radio luminosity functions at 325 MHz for a sample of AGN and star-forming galaxies by matching a 138 deg sq. radio survey conducted with the Giant Metrewave Radio Telescope (GMRT), with optical imaging and redshifts from the Galaxy And Mass Assembly (GAMA) survey. We find that the radio luminosity function at 325 MHz for star-forming galaxies closely follows that measured at 1.4 GHz. By fitting the AGN radio luminosity function out to $z = 0.5$ as a double power law, and parametrizing the evolution as ${\Phi} \propto (1 + z)^{k}$ , we find evolution parameters of $k = 0.92 \pm 0.95$ assuming pure density evolution and $k = 2.13 \pm 1.96$ assuming pure luminosity evolution. We find that the Low Excitation Radio Galaxies are the dominant population in space density at lower luminosities. Comparing our 325 MHz observations with radio continuum imaging at 1.4 GHz, we determine separate radio luminosity functions for steep and flat-spectrum AGN, and show that the beamed population of flat-spectrum sources in our sample can be shifted in number density and luminosity to coincide with the unbeamed population of steep-spectrum sources, as is expected in the orientation based unification of AGN.
This review covers four current questions in the behavior of the atomic and molecular interstellar medium. These include whether the atomic gas originates primarily in cold streams or hot flows onto galaxies; what the filling factor of cold gas actually is in galactic regions observationally determined to be completely molecular; whether molecular hydrogen determines or merely traces star formation; and whether gravity or turbulence drives the dynamical motions observed in interstellar clouds, with implications on their star formation properties.
In the current concordance cosmology small halos are expected to be completely dark and can significantly perturb low-mass galaxies during minor merger interactions. These interactions may well contribute to the diversity of the dwarf galaxy population. Dwarf galaxies in the field are often observed to have peculiarities in their structure, morphology, and kinematics as well as strong bursts of star formation without apparent cause. We aim to characterize the signatures of minor mergers of dwarf galaxies with dark satellites to aid their observational identification. We explore and quantify a variety of structural, morphological, and kinematic indicators of merging dwarf galaxies and their remnants using a suite of hydrodynamical simulations. The most sensitive indicators of mergers with dark satellites are large asymmetries in the gaseous and stellar distributions, enhanced central surface brightness and starbursts, and velocity offsets and misalignments between the cold gas and stellar components. In general merging systems span a wide range of values of the most commonly used indicators, while isolated objects tend to have more confined values. Interestingly, we find in our simulations that a significantly off-centered burst of star formation can pinpoint the location of the dark satellite. Observational systems with such characteristics are perhaps the most promising for unveiling the presence of the hitherto, missing satellites.
We study the radio properties at 1.4 GHz of Seyfert galaxies with strong forbidden high-ionization lines (FHILs), selected from the Sloan Digital Sky Survey - a large-sized sample containing nearly equal proportion of diverse range of Seyfert galaxies showing similar redshift distributions compiled by Gelbord et al. (2009) using the Very Large Array survey images. The radio detection rate is low, 49%, which is lower than the detection rate of several other known Seyfert galaxy samples. These galaxies show low star formation rates and the radio emission is dominated by the active nucleus with $\le$10% contribution from thermal emission, and possibly, none show evidence for relativistic beaming. The radio detection rate, distributions of radio power, and correlations between radio power and line luminosities or X-ray luminosity for narrow-line Seyfert 1 (NLS1), Seyfert 1 and Seyfert 2 galaxies are consistent with the predictions of the unified scheme hypothesis. Using correlation between radio and [O\,III]\,$\lambda$ \,5007\,\AA\ luminosities, we show that $\sim$8% sample sources are radio-intermediate and the remaining are radio-quiet. There is possibly an ionization stratification associated with clouds on scales of 0.1-1.0 kpc, which have large optical depths at 1.4 GHz, and it seems these clouds are responsible for free-free absorption of radio emission from the core, hence, leading to low radio detection rate for these FHIL-emitting Seyfert galaxies.
On-the-fly mapping of cm-wave spectral lines has been implemented at the the Tidbinbilla 70-m radio antenna. We describe the implementation and data reduction procedure and present new H92$\alpha$ radio recombination line maps towards Orion A and Sagittarius A. Comparison of the Orion~A map to previous observations suggests that the lines arise largely from gas with electron density of 100--200\,cm$^{-3}$. On-the-fly mapping is very efficient at generating large maps of bright lines (such as radio recombination lines), but will still yield strong efficiency gains for smaller maps of fainter lines, such as the ammonia inversion lines at the 1.3\,cm wavelength.
We present high-resolution multiwavelength radio continuum images of the region within 150$"$ of Sgr A*, revealing a number of new extended features and stellar sources in this region. First, we detect a continuous 2" east-west ridge of radio emission, linking Sgr A* and a cluster of stars associated with IRS 13N and IRS 13E. The ridge suggests that an outflow of east-west blob-like structures is emerging from Sgr A*. We also find arc-like features within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. We use near-IR fluxes to show that the emission has similar characteristics to those of a protoplanetary disk irradiated by the intense radiation field at the Galactic center. This suggests that star formation has taken place within the S cluster 2$"$ from Sgr A*. We suggest that the diffuse X-ray emission associated with Sgr A* is due to an expanding hot wind produced by the mass loss from B-type main sequence stars, and/or the disks of photoevaporation of low mass YSOs at a rate ~10^{-6} solar mass per year. The proposed model naturally reduces the inferred accretion rate and is an alternative to the inflow-outflow style models to explain the underluminous nature of Sgr A*. Second, we detect new cometary radio and nea-IR sources and a striking tower of radio emission suggesting that they are tracing interaction sites of a mildly relativistic jet from Sgr A* with the atmosphere of stars and the nonthermal Sgr A East shell at a PA$\sim50-60^\circ$ with ~10^{-7} solar mass per year, and opening angle 10 degrees.
The 1$_{11}$-1$_{01}$ lines of ortho and para--NH$_2$D (o/p-NH$_2$D), respectively at 86 and 110 GHz, are commonly observed to provide constraints on the deuterium fractionation in the interstellar medium. In cold regions, the hyperfine structure due to the nitrogen ($^{14}$N) nucleus is resolved. To date, this splitting is the only one which is taken into account in the NH$_2$D column density estimates. We investigate how the inclusion of the hyperfine splitting caused by the deuterium (D) nucleus affects the analysis of the rotational lines of NH$_2$D. We present 30m IRAM observations of the above mentioned lines, as well as APEX o/p-NH$_2$D observations of the 1$_{01}$-0$_{00}$ lines at 333 GHz. The hyperfine spectra are first analyzed with a line list that only includes the hyperfine splitting due to the $^{14}$N nucleus. We find inconsistencies between the line widths of the 1$_{01}$-0$_{00}$ and 1$_{11}$-1$_{01}$ lines, the latter being larger by a factor of $\sim$1.6$\pm0.3$. Such a large difference is unexpected given the two sets of lines are likely to originate from the same region. We next employ a newly computed line list for the o/p-NH$_2$D transitions, where the hyperfine structure induced by both nitrogen and deuterium nuclei is included. With this new line list, the analysis of the previous spectra leads to linewidths which are compatible. Neglecting the hyperfine structure owing to D leads to overestimate the linewidths of the o/p-NH$_2$D lines at 3 mm. The error for a cold molecular core is about 50\%. This error propagates directly to the column density estimate. It is therefore recommended to take into account the hyperfine splittings caused by both the $^{14}$N and D nuclei in any analysis relying on these lines.
In the central regions of active galaxies, dense molecular medium are exposed to various types of radiation and energy injections, such as UV, X-ray, cosmic ray, and shock dissipation. With the rapid progress of chemical models and implementation of new-generation mm/submm interferometry, we are now able to use molecules as powerful diagnostics of the physical and chemical processes in galaxies. Here we give a brief overview on the recent ALMA results to demonstrate how molecules can reveal underlying physical and chemical processes in galaxies. First, new detections of Galactic molecular absorption systems with elevated HCO/H$^{13}$CO$^+$ column density ratios are reported, indicating that these molecular media are irradiated by intense UV fields. Second, we discuss the spatial distributions of various types of shock tracers including HNCO, CH$_3$OH and SiO in NGC 253 and NGC 1068. Lastly, we provide an overview of proposed diagnostic methods of nuclear energy sources using ALMA, with an emphasis on the synergy with sensitive mid-infrared spectroscopy, which will be implemented by JWST and SPICA to disentangle the complex nature of heavily obscured galaxies across the cosmic time.
We have conducted 1.1 mm ALMA observations of a contiguous $105'' \times 50''$ or 1.5 arcmin$^2$ window in the SXDF-UDS-CANDELS. We achieved a 5$\sigma$ sensitivity of 0.28 mJy, providing a flat sensus of dusty star-forming galaxies with $L_{\rm IR} \sim6\times10^{11}$ $L_\odot$ (for $T_{\rm dust}$ =40K) up to $z\sim10$ thanks to the negative K-correction at this wavelength. We detected 5 brightest sources (S/N$>$6) and 18 low-significance sources (5$>$S/N$>$4; these may contain spurious detections, though). One of the 5 brightest ALMA sources ($S_{\rm 1.1mm} = 0.84 \pm 0.09$ mJy) is extremely faint in the WFC3 and VLT/HAWK-I images, demonstrating that a contiguous ALMA imaging survey is able to uncover a faint dust-obscured population that is invisible in deep optical/near-infrared surveys. We found a possible [CII]-line emitter at $z=5.955$ or a low-$z$ CO emitting galaxy within the field, which may allow us to constrain the [CII] and/or the CO luminosity functions across the history of the universe.
We present deep H$\alpha$ imaging of three nearby dwarf galaxies, carefully selected to optimize observations with the Maryland-Magellan Tunable Filter (MMTF) on the Magellan 6.5m telescope. An effective bandpass of $\sim$13\AA\ is used, and the images reach 3$\sigma$ flux limits of $\sim$8$\times10^{-18}$ ergs s$^{-1}$ cm$^{-2}$, which is about an order of magnitude lower than standard narrowband observations obtained by the most recent generation of local H$\alpha$ galaxy surveys. The observations were originally motivated by the finding that the H$\alpha$/FUV flux ratio of galaxies systematically declines as global galactic properties such as the star formation rate and stellar mass decrease. The three dwarf galaxies selected for study have star formation rates, that when calculated from their H$\alpha$ luminosities using standard conversion recipes, are $\sim$50\% of those based on the FUV. Follow-up studies of many of the potential causes for the trends in the H$\alpha$/FUV flux ratio have been performed, but the possibility that previous observations have missed a non-negligible fraction of faint ionized emission in dwarf galaxies has not been investigated. The MMTF observations reveal both diffuse and structured H$\alpha$ emission (filaments, shells, possible single-star HII regions) spanning extents up to 2.5 times larger relative to previous observations. However, only up to an additional $\sim5$\% of H$\alpha$ flux is captured, which does not account for the trends in the H$\alpha$/FUV ratio. Beyond investigation of the H$\alpha$/FUV ratio, the impact of the newly detected extended flux on our understanding of star formation, the properties of HII regions, and the propagation of ionizing photons warrant further investigation.
The dust attenuation for a sample of $\sim$10000 local ($z\lesssim0.1$) star forming galaxies is constrained as a function of their physical properties. We utilize aperture-matched multi-wavelength data available from the Galaxy Evolution Explorer (GALEX) and the Sloan Digital Sky Survey (SDSS) to ensure that regions of comparable size in each galaxy are being analyzed. We follow the method of Calzetti et al. (1994) and characterize the dust attenuation through the UV power-law index, $\beta$, and the dust optical depth, which is quantified using the difference in Balmer emission line optical depth, $\tau_B^l=\tau_{\mathrm{H}\beta} - \tau_{\mathrm{H}\alpha}$. The observed linear relationship between $\beta$ and $\tau_B^l$ is similar to the local starburst relation, but the large scatter ($\sigma_{\mathrm{int}}=0.44$) suggests there is significant variation in the local Universe. We derive a selective attenuation curve over the range $1250\mathrm{\AA}<\lambda<8320\mathrm{\AA}$ and find that a single attenuation curve is effective for characterizing the majority of galaxies in our sample. This curve has a slightly lower selective attenuation in the UV compared to previously determined curves. We do not see evidence to suggest that a 2175\AA\ feature is significant in the average attenuation curve. Significant positive correlations are seen between the amount of UV and optical reddening and galaxy metallicity, mass, star formation rate (SFR), and SFR surface density. This provides a potential tool for gauging attenuation where the stellar population is unresolved, such as at high-$z$.
The origin of short timescale (weeks/months) variability of AGN, whether due to intrinsic disc variations or reprocessing of X-ray emission by a surrounding accretion disc, has been a puzzle for many years. However recently a number of observational programmes, particularly of NGC5548 with Swift, have shown that the UV/optical variations lag behind the X-ray variations in a manner strongly supportive of X-ray reprocessing. Somewhat surprisingly the implied size of the accretion disc is ~3x greater than expected from a standard, smooth, Shakura-Sunyaev thin disc model. Although the difference may be explained by a clumpy accretion disc, it is not clear whether the difference will occur in all AGN or whether it may change as, eg, a function of black hole mass, accretion rate or disc temperature. Measurements of interband lags for most AGN require long timescale monitoring, which is hard to arrange. However for low mass (<1 million solar mass) AGN, the combination of XMM-Newton EPIC (X-rays) with the optical monitor in fast readout mode allows an X-ray/UV-optical lag to be measured within a single long observation. Here we summarise previous related observations and report on XMM-Newton observations of NGC4395 (mass ~100x lower and accretion rate ~20x lower than for NGC5548). We find that the UVW1 lags the X-rays by ~470s. Simultaneous observations at 6 different ground based observatories also allowed the g-band lag (~800s) to be measured. These observations are in agreement with X-ray reprocessing but initial analysis suggests that, for NGC4395, they do not differ markedly from the predictions of the standard thin disc model.
Gravitational lensing is a fundamental tool for cosmology. A recent
instrument which will provide more information for models of these objects is
ALMA. Our goal is to select lens candidates to observe with ALMA and then model
them using GravLens Software. We had selected 12 quadruple images systems from
the CASTLES database, which show a high probability of observing extended
sources in the submillimetric range. These new data will allow us to improve
existing models.
Las lentes gravitatorias son una herramienta fundamental para la
cosmolog\'ia. Un nuevo instrumento que nos proporcionar\'a mayor informaci\'on
para los modelos de estos objetos, es ALMA. Nuestro objetivo es seleccionar
lentes candidatas para observar con ALMA y posteriormente modelarlas mediante
el programa GravLens. Seleccionamos de la base de datos de CASTLES, 12 sistemas
cu\'adruples, los cuales tienen mayor probabilidad de observar fuentes
extendidas en el rango submilim\'etrico. Estos nuevos datos nos permitir\'an
mejorar los modelos exitentes para dichos sistemas.
We study gravitational collapse of low-metallicity gas clouds and the formation of protostars by three-dimensional hydrodynamic simulations. Grain growth, non-equilibrium chemistry, molecular cooling, and chemical heating are solved in a self-consistent manner for the first time. We employ the realistic initial conditions for the abundances of metal and dust, and the dust size distribution obtained from recent Population III supernova calculations. We also introduce the state-of-the-art particle splitting method based on the Voronoi tessellation and achieve an extremely high mass resolution of ~10^{-5} Msun (10 earth masses) in the central region. We follow the thermal evolution of several early clouds with various metallicities. We show that the condition for cloud fragmentation depends not only on the gas metallicity but also on the collapse timescale. In many cases, the cloud fragmentation is prevented by the chemical heating owing to molecular hydrogen formation even though dust cooling becomes effective. Meanwhile, in several cases, efficient OH and H2O cooling promotes the cloud elongation, and then cloud "filamentation" is driven by dust thermal emission as a precursor of eventual fragmentation. While the filament fragmentation is driven by rapid gas cooling with >10^{-5} Zsun, fragmentation occurs in a different manner by the self-gravity of a circumstellar disk with <10^{-5} Zsun. We use a semi-analytic model to estimate the number fraction of the clouds which undergo the filament fragmentation to be a several percents with 10^{-5}--10^{-4} Zsun. Overall, our simulations show a viable formation path of the recently discovered Galactic low-mass stars with extremely small metallicities.
We present deep 15.7-GHz observations made with the Arcminute Microkelvin Imager Large Array in two fields previously observed as part of the Tenth Cambridge (10C) survey. These observations allow the source counts to be calculated down to 0.1 mJy, a factor of five deeper than achieved by the 10C survey. The new source counts are consistent with the extrapolated fit to the 10C source count, and display no evidence for either steepening or flattening of the counts. There is thus no evidence for the emergence of a significant new population of sources (e.g. starforming) at 15.7 GHz flux densities above 0.1 mJy, the flux density level at which we expect starforming galaxies to begin to contribute. Comparisons with the de Zotti et al. model and the SKADS Simulated Sky show that they both underestimate the observed number of sources by a factor of two at this flux density level. We suggest that this is due to the flat-spectrum cores of radio galaxies contributing more significantly to the counts than predicted by the models.
(Abridged) Aims. We derive the physical properties of a filament discovered in the dark cometary-shaped cloud L1251. Methods. Mapping observations in the NH3(1,1) and (2,2) inversion lines, encompassing 300 positions toward L1251, were performed with the Effelsberg 100-m telescope at a spatial resolution of 40 arcsec and a spectral resolution of 0.045 km/s. Results. The filament L1251A consists of three condensations (alpha, beta, and gamma) of elongated morphology, which are combined in a long and narrow structure covering a 38 arcmin by 3 arcmin angular range. The opposite chirality (dextral and sinistral) of the alpha+beta and gamma condensations indicates magnetic field helicities of two types, negative and positive, which were most probably caused by dynamo mechanisms. We estimated the magnetic Reynolds number Rm > 600 and the Rossby number R < 1, which means that dynamo action is important.
We address the relation between star formation and AGN activity in a sample of 231 nearby ($0.0002<z<0.0358$) early type galaxies by carrying out a multi-wavelength study using archival observations in the UV, IR and radio. Our results indicate that early type galaxies in the current epoch are rarely powerful AGNs, with $P<10^{22}\,WHz^{-1}$ for a majority of the galaxies. Only massive galaxies are capable of hosting powerful radio sources while less massive galaxies are hosts to lower radio power sources. Evidence of ongoing star formation is seen in approximately 7% of the sample. The SFR of these galaxies is less than 0.1 $M_{\odot}yr^{-1}$. They also tend to be radio faint ($P<10^{22}\,WHz^{-1}$). There is a nearly equal fraction of star forming galaxies in radio faint ($P<10^{22}\,WHz^{-1}$) and radio bright galaxies ($P\geq10^{22}\,WHz^{-1}$) suggesting that both star formation and radio mode feedback are constrained to be very low in our sample. We notice that our galaxy sample and the Brightest Cluster Galaxies (BCGs) follow similar trends in radio power versus SFR. This may be produced if both radio power and SFR are related to stellar mass.
We have analyzed the angular momentum of the molecular cloud cores in the Orion A giant molecular cloud observed in the N2H+ J = 1-0 line with the Nobeyama 45 m radio telescope. We have measured the velocity gradient using position velocity diagrams passing through core centers, and made sinusoidal fitting against the position angle. 27 out of 34 N2H+ cores allowed us to measure the velocity gradient without serious confusion. The derived velocity gradient ranges from 0.5 to 7.8 km/s/pc. We marginally found that the specific angular momentum J/M (against the core radius R) of the Orion N2H+ cores tends to be systematically larger than that of molecular cloud cores in cold dark clouds obtained by Goodman et al., in the J/M-R relation. The ratio beta of rotational to gravitational energy is derived to be beta = 10^{-2.3+/-0.7}, and is similar to that obtained for cold dark cloud cores in a consistent definition. The large-scale rotation of the integral-shaped filament of the Orion A giant molecular cloud does not likely govern the core rotation at smaller scales.
We investigate the growth histories of dark matter halos associated with dwarf satellites in Local Group galaxies and the resultant evolution of the baryonic component. Our model is based on the recently proposed property that the mean surface density of a dark halo inside a radius at maximum circular velocity $V_{\rm max}$ is universal over a large range of $V_{\rm max}$. Following that this surface density of 20 $M_{\odot}$~pc$^{-2}$ well explains dwarf satellites in the Milky Way and Andromeda, we find that the evolution of the dark halo in this common surface-density scale is characterized by the rapid increase of the halo mass assembled by the redshift $z_{\rm TT}$ of the tidal truncation by its host halo, at early epochs of $z_{\rm TT} \gsim 6$ or $V_{\rm max} \lsim 22$ km~s$^{-1}$. This mass growth of the halo is slow at lower $z_{\rm TT}$ or larger $V_{\rm max}$. Taking into account the baryon content in this dark halo evolution, under the influence of the ionizing background radiation, we find that the dwarf satellites are divided into roughly two families: those with $V_{\rm max} \lsim 22$ km~s$^{-1}$ having high star formation efficiency and those with larger $V_{\rm max}$ having less efficient star formation. This semi-analytical model is in good agreement with the high-resolution numerical simulation for galaxy formation and with the observed star formation histories for Fornax and Leo~II. This suggests that the evolution of a dark halo plays a key role in understanding star formation histories in dwarf satellites.
We study the diffuse X-ray luminosity ($L_X$) of star forming galaxies using 2-D axisymmetric hydrodynamical simulations and analytical considerations of supernovae (SNe) driven galactic outflows. We find that the mass loading of the outflows, a crucial parameter for determining the X-ray luminosity, is constrained by the availability of gas in the central star forming region, and a competition between cooling and expansion. We show that the allowed range of the mass loading factor can explain the observed scaling of $L_X$ with star formation rate (SFR) as $L_X \propto$ SFR$^2$ for SFR $\gtrsim 1$ M$_\odot$yr$^{-1}$, and a flatter relation at low SFRs. We also show that the emission from the hot circumgalactic medium (CGM) in the halo of massive galaxies can explain the sub-linear behaviour of the $L_X-$SFR relation as well as a large scatter in the diffuse X-ray emission for low SFRs ($\lesssim$ few M$_\odot$yr$^{-1}$). Our results point out that galaxies with small SFRs and large diffuse X-ray luminosities are excellent candidates for detection of the elusive CGM.
I have used a Monte Carlo model for dust scattering in our Galaxy with multiple scattering to study the diffuse emission seen by the \galex\ mission. I find that the emission at low and mid latitudes is fit well by scattering from dust grains with an albedo of 0.4 and $g = 0$ (isotropically scattering grains). However, only about 30\%\ of the diffuse radiation at high Galactic latitudes is due to dust scattering. There is an additional component of 500 - 600 photons cm$^{-2}$ s$^{-1}$ sr$^{-1}$ \AA$^{-1}$ at all latitudes of an unknown origin.
We use self-consistent numerical simulations of the evolution and disruption of the Sun's birth cluster in the Milky Way potential to investigate the present-day phase space distribution of the Sun's siblings. The simulations include the gravitational N-body forces within the cluster and the effects of stellar evolution on the cluster population. In addition the gravitational forces due to the Milky Way potential are accounted for in a self-consistent manner. Our aim is to understand how the astrometric and radial velocity data from the Gaia mission can be used to pre-select solar sibling candidates. We vary the initial conditions of the Sun's birth cluster, as well as the parameters of the Galactic potential. We show that the disruption time-scales of the cluster are insensitive to the details of the non-axisymmetric components of the Milky Way model and we make predictions, averaged over the different simulated possibilities, about the number of solar siblings that should appear in surveys such as Gaia or GALAH. We find a large variety of present-day phase space distributions of solar siblings, which depend on the cluster initial conditions and the Milky Way model parameters. We show that nevertheless robust predictions can be made about the location of the solar siblings in the space of parallaxes ($\varpi$), proper motions ($\mu$) and radial velocities ($V_\mathrm{r}$). By calculating the ratio of the number of simulated solar siblings to that of the number of stars in a model Galactic disk, we find that this ratio is above 0.5 in the region given by: $\varpi \geq 5$mas, $4 \leq \mu \leq 6$masyr$^{-1}$, and $-2\leq V_\mathrm{r} \leq 0$kms$^{-1}$. Selecting stars from this region should increase the probability of success in identifying solar siblings through follow up observations [Abridged].
Context. Pisces A & Pisces B are the only two galaxies found via optical imaging and spectroscopy out of 22 HI clouds identified in the GALFAHI survey as dwarf galaxy candidates. Aims. Derive the HI content and kinematics of Pisces A & B. Methods. Aperture synthesis HI observations using the seven dish Karoo Array Telescope (KAT-7), which is a pathfinder instrument for MeerKAT, the South African precursor to the mid-frequency Square Kilometre Array (SKA-MID). Results. The small rotation velocities detected of ~5 km/sec and ~10 km/sec in Pisces A & B respectively, and their HI content show that they are really dwarf irregular galaxies (dIrr). Despite that small rotation component, it is more the random motions ~9-11 km/sec that provide most of the gravitational support, especially in the outer parts. The study of their kinematics, especially the strong gradients of random motions, suggest that those two dwarf galaxies are not yet in equilibrium. Conclusions. These HI rich galaxies may be indicative of a large population of dwarfs at the limit of detectability. However, such gas-rich dwarf galaxies will most likely never be within the virial radius of MW-type galaxies and become sub-halo candidates. Systems such as Pisces A & B are more likely to be found at a few Mpc.s from MW-type galaxies.
Within a cluster, gravitational effects can lead to the removal of stars from their parent galaxies. Gas hydrodynamical effects can additionally strip gas and dust from galaxies. The properties of the ICL can therefore help constrain the physical processes at work in clusters by serving as a fossil record of the interaction history. The present study is designed to characterise this ICL in a ~10^14 M_odot and z~0.53 cluster of galaxies from imaging and spectroscopic points of view. By applying a wavelet-based method to CFHT Megacam and WIRCAM images, we detect significant quantities of diffuse light. These sources were then spectroscopically characterised with MUSE. MUSE data were also used to compute redshifts of 24 cluster galaxies and search for cluster substructures. An atypically large amount of ICL has been detected in this cluster. Part of the detected diffuse light has a very weak optical stellar component and apparently consists mainly of gas emission, while other diffuse light sources are clearly dominated by old stars. Furthermore, emission lines were detected in several places of diffuse light. Our spectral analysis shows that this emission likely originates from low-excitation parameter gas. The stellar contribution to the ICL is about 2.3x10^9 yrs old even though the ICL is not currently forming a large number of stars. On the other hand, the contribution of the gas emission to the ICL in the optical is much greater than the stellar contribution in some regions, but the gas density is likely too low to form stars. These observations favour ram pressure stripping, turbulent viscous stripping, or supernovae winds as the origin of the large amount of intracluster light. Since the cluster appears not to be in a major merging phase, we conclude that ram pressure stripping is the most plausible process that generates the observed ICL sources.
The Sloan Digital Sky Survey (SDSS) discovered a few unusual quasars with a characteristic break in the continuum around 3000 A that neither shows the typical structure of broad absorption line (BAL) troughs nor is explained by typical intrinsic dust reddening. We used the method of Kohonen self-organising maps for a systematical search for quasars with such properties in the SDSS spectra archive. We constructed a sample of 23 quasars classified as 3000 A break quasars and two comparison samples of quasars with similar properties, to some extent, but also showing typical BAL features. We computed ensemble-averaged broad-band SEDs based on archival data from SDSS, GALEX, 2MASS, UKIDSS, and WISE. The SEDs were corrected for intrinsic dust absorption by the comparison with the average SED of normal quasars. The de-reddened arithmetic median composite SED of the 3000 A break quasars is found to be indistinguishable from that of the unusual BAL quasars. We conclude that 3000 A break quasars are most likely extreme versions of BAL quasars. Assuming that the intrinsic SED of the continuum source is represented by the quasar composite SED, the 3000 A break quasars tend to be intrinsically more luminous than ordinary quasars. (Abstract modified to match the arXiv format.)
Recent models for the large-scale Galactic magnetic fields in the literature were largely constrained by synchrotron emission and Faraday rotation measures. We select three different but representative models and compare their predicted polarized synchrotron and dust emission with that measured by the Planck satellite. We first update these models to match the Planck synchrotron products using a common model for the cosmic-ray leptons. We discuss the impact on this analysis of the ongoing problems of component separation in the Planck microwave bands and of the uncertain cosmic-ray spectrum. In particular, the inferred degree of ordering in the magnetic fields is sensitive to these systematic uncertainties. We then compare the resulting simulated emission to the observed dust emission and find that the dust predictions do not match the morphology in the Planck data, particularly the vertical profile in latitude. We show how the dust data can then be used to further improve these magnetic field models, particularly in the thin disc of the Galaxy where the dust is concentrated. We demonstrate this for one of the models and present it as a proof of concept for how we will advance these studies in future using complementary information from ongoing and planned observational projects.
Since the first detection of intracluster planetary nebulae in 1996, imaging and spectroscopic surveys identified such stars to trace the radial extent and the kinematics of diffuse light in clusters. This topic of research is tightly linked with the studies of galaxy formation and evolution in dense environment, as the spatial distribution and kinematics of planetary nebulae in the outermost regions of galaxies and in the cluster cores is relevant for setting constraints on cosmological simulations. In this sense, extragalactic planetary nebulae play a very important role in the near-field cosmology, in order to measure the integrated mass as function of radius and the orbital distribution of stars in structures placed in the densest regions of the nearby universe.
Supermassive black holes (BHs) of millions solar masses and above reside in the center of most local galaxies, but they also power active galactic nuclei and quasars, detected up to z=7. This observational evidence puts strong constraints on the BH growth and the mass of the first BH seeds. The scenario of "direct collapse" is very appealing as it leads to the formation of large mass BH seeds in the range 10^4-10^6 Msun, which eases explaining how quasars at z=6-7 are powered by BHs with masses >10^9 Msun. Direct collapse, however, appears to be rare, as the conditions required by the scenario are that gas is metal-free, the presence of a strong photo-dissociating Lyman-Werner flux, and large inflows of gas at the center of the halo, sustained for 10-100 Myr. We performed several cosmological hydrodynamical simulations that cover a large range of box sizes and resolutions, thus allowing us to understand the impact of several physical processes on the distribution of direct collapse BHs. We identify halos where direct collapse can happen, and derive the number density of BHs. We also investigate the discrepancies between hydrodynamical simulations, direct or post-processed, and semi-analytical studies. We find that for direct collapse to account for BHs in normal galaxies, the critical Lyman-Werner flux required for direct collapse must be much less than predicted by 3D simulations that include detailed chemical models. However, when supernova feedback is relatively weak, enough direct collapse BHs to explain z=6-7 quasars can be obtained for more realistic values of the critical Lyman Werner flux.
We derive the stellar mass fraction in the galaxy cluster RXC J2248.7-4431 observed with the Dark Energy Survey (DES) during the Science Verification period. We compare the stellar mass results from DES (5 filters) with those from the Hubble Space Telescope CLASH (17 filters). When the cluster spectroscopic redshift is assumed, we show that stellar masses from DES can be estimated within 25% of CLASH values. We compute the stellar mass contribution coming from red and blue galaxies, and study the relation between stellar mass and the underlying dark matter using weak lensing studies with DES and CLASH. An analysis of the radial profiles of the DES total and stellar mass yields a stellar-to-total fraction of f*=7.0+-2.2x10^-3 within a radius of r_200c~3 Mpc. Our analysis also includes a comparison of photometric redshifts and star/galaxy separation efficiency for both datasets. We conclude that space-based small field imaging can be used to calibrate the galaxy properties in DES for the much wider field of view. The technique developed to derive the stellar mass fraction in galaxy clusters can be applied to the ~100 000 clusters that will be observed within this survey. The stacking of all the DES clusters would reduce the errors on f* estimates and deduce important information about galaxy evolution.
The metallicity distribution function of globular clusters (GCs) in galaxies is a key to understanding galactic formation and evolution. The calcium II triplet (CaT) index has recently become a popular metal abundance indicator thanks to its sensitivity to GC metallicity. Here we revisit and assess the reliability of CaT as a metallicity indicator using our new stellar population synthesis simulations based on empirical, high-resolution fluxes. The model shows that the CaT strength of old ($>$ 10 Gyr) GCs is proportional to ${\rm [Fe/H]}$ below $-0.5$. In the modest metal-rich regime, however, CaT does not increase anymore with ${\rm [Fe/H]}$ due to the little contribution from coolest red giant stars to the CaT absorption. The nonlinear nature of the color--$CaT$ relation is confirmed by the observations of GCs in nearby early-type galaxies. This indicates that the CaT should be used carefully when deriving metallicities of metal-rich stellar populations. Our results offer an explanation for the observed sharp difference between the color and $CaT$ distributions of GCs in the same galaxies. We take this as an analogy to the view that metallicity--color and metallicity--Lick index nonlinearity of GCs is primarily responsible for their observed "bimodal" distributions of colors and absorption indices.
Context. To investigate the dynamical properties of protostellar jets. Aims. Determine the proper motion of protostellar jets around Class 0 and Class I sources in an active star forming region in Serpens. Methods. Multi-epoch deep images in the 2.122 $\mu$m line of molecular hydrogen, v=1-0 S(1), obtained with the near-infrared instrument NOTCam over a time-scale of 10 years, are used to determine proper motion of knots and jets. K-band spectroscopy of the brighter knots is used to supply radial velocities, estimate extinction, excitation temperature, and H$_2$ column densities towards these knots. Results. We measure the proper motion of 31 knots over different time scales (2, 4, 6, and 10 years). The typical tangential velocity is around 50 km/s for the 10 year base-line, but for shorter time-scales a maximum tangential velocity up to 300 km/s is found for a few knots. Based on morphology, velocity information and the locations of known protostars, we argue for the existence of at least three partly overlapping and deeply embedded flows, one Class 0 flow and two Class I flows. The multi-epoch proper motion results indicate time-variable velocities of the knots, for the first time directly measured for a Class 0 jet. We find in general higher velocities for the Class 0 jet than for the two Class I jets. While the bolometric luminosites of the three driving sources are about equal, the derived mass flow rate (dM/dt)$_{\rm out}$ is two orders of magnitude higher in the Class 0 flow than in the two Class I flows.
This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the solar system, the Milky Way, galaxy evolution, quasars, and other topics. In addition, we show that if the cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 Trans Neptunian Objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).
Aims: Using the unprecedented combination of high resolution and sensitivity offered by ALMA, we aim to investigate whether and how hot corinos, circumstellar disks, and ejected gas are related in young solar-mass protostars. Methods: We observed CH$_3$CHO and deuterated water (HDO) high-excitation ($E_{\rm u}$ up to 335 K) lines towards the Sun-like protostar HH212--MM1. Results: For the first time, we have obtained images of CH$_3$CHO and HDO emission in the inner $\simeq$ 100 AU of HH212. The multifrequency line analysis allows us to contrain the density ($\geq$ 10$^{7}$ cm$^{-3}$), temperature ($\simeq$ 100 K), and CH$_3$CHO abundance ($\simeq$ 0.2--2 $\times$ 10$^{-9}$) of the emitting region. The HDO profile is asymmetric at low velocities ($\leq$ 2 km s$^{-1}$ from $V_{\rm sys}$). If the HDO line is optically thick, this points to an extremely small ($\sim$ 20--40 AU) and dense ($\ge$ 10$^{9}$ cm$^{-3}$) emitting region. Conclusions: We report the first detection of a hot corino in Orion. The HDO asymmetric profile indicates a contribution of outflowing gas from the compact central region, possibly associated with a dense disk wind.
We compare the properties of stellar populations of model galaxies from the Cosmic Reionization On Computers (CROC) project with the exiting UV and IR data. Since CROC simulations do not follow cosmic dust directly, we adopt two variants of the dust-follows-metals ansatz to populate model galaxies with dust. Using the dust radiative transfer code Hyperion, we compute synthetic stellar spectra, UV continuum slopes, and IR fluxes for simulated galaxies. We find that the simulation results generally match observational measurements, but, perhaps, not in full detail. The differences seem to indicate that our adopted dust-follows-metals ansatzes are not fully sufficient. While the discrepancies with the exiting data are marginal, the future JWST data will be of much higher precision, rendering highly significant any tentative difference between theory and observations. It is, therefore, likely, that in order to fully utilize the precision of JWST observations, fully dynamical modeling of dust formation, evolution, and destruction may be required.
Links to: arXiv, form interface, find, astro-ph, recent, 1601, contact, help (Access key information)
We have studied high mass X-ray binary (HMXB) populations within two low-metallicity, starburst galaxies, Haro 11 and VV 114. These galaxies serve as analogs to high-redshift (z>2) Lyman break galaxies, and within the larger sample of Lyman break analogs (LBAs) are sufficiently nearby (<87 Mpc) to be spatially-resolved by Chandra. Previous studies of the X-ray emission in LBAs have found that the 2-10 keV luminosity per star formation rate (SFR) in these galaxies is elevated, potentially because of their low metallicities (12+log[O/H]= 8.3-8.4). Theoretically, the progenitors of XRBs forming in lower metallicity environments lose less mass from stellar winds over their lifetimes, producing more massive compact objects (i.e., neutron stars and black holes), and thus resulting in more numerous and luminous HMXBs per SFR. We have performed an in-depth study of the only two LBAs that have spatially-resolved 2-10 keV emission with Chandra to present the bright end of the X-ray luminosity distribution of HMXBs (L$_X>10^{39}$ erg/s; ultraluminous X-ray sources, ULXs) in these low-metallicity galaxies, based on 8 detected ULXs. Comparing with the star-forming galaxy X-ray luminosity function (XLF) presented by Mineo et al. (2012), Haro 11 and VV 114 host ~4 times more L$_X>10^{40}$ erg/s sources than expected given their SFRs. We simulate the effects of source blending from crowded lower luminosity HMXBs using the star-forming galaxy XLF and then vary the XLF shapes until we reproduce the observed point source luminosity distributions. We find that these LBAs have a shallower bright end slope than the standard XLF. If we conservatively assume that the brightest X-ray source from each galaxy is powered by an AGN rather than a HMXB and eliminate these sources from consideration, the luminosity distribution becomes poorly constrained but does appear to be consistent with a standard XLF. [Abridged]
Megamaser disks provide the most precise and accurate extragalactic supermassive black hole masses. Here we describe a search for megamasers in nearby galaxies using the Green Bank Telescope (GBT). We focus on galaxies where we believe that we can resolve the gravitational sphere of influence of the black hole and derive a stellar or gas dynamical measurement with optical or NIR observations. Since there are only a handful of super massive black holes (SMBH) that have direct black hole mass measurements from more than one method, even a single galaxy with a megamaser disk and a stellar dynamical black hole mass would provide necessary checks on the stellar dynamical methods. We targeted 87 objects from the Hobby-Eberly Telescope Massive Galaxy Survey, and detected no new maser disks. Most of the targeted objects are elliptical galaxies with typical stellar velocity dispersions of 250 km/s and distances within 130 Mpc. We discuss the implications of our non-detections, whether they imply a threshold X-ray luminosity required for masing, or possibly reflect the difficulty of maintaining a masing disk around much more massive (>10^8 Msun) black holes at low Eddington ratio. Given the power of maser disks at probing black hole accretion and demographics, we suggest that future maser searches should endeavour to remove remaining sample biases, in order to sort out the importance of these covariant effects.
In the coming decade the Gaia satellite will precisely measure the positions and velocities of millions of stars in the Galactic halo, including stars in many tidal streams. These streams, the products of hierarchical accretion of satellite galaxies by the Milky Way (MW), can be used to infer the Galactic gravitational potential thanks to their initial compactness in phase space. Plans for observations to extend Gaia's radial velocity (RV) measurements to faint stars, and to determine precise distances to RR Lyrae (RRLe) in streams, would further extend the power of Gaia's kinematic catalog to characterize the MW's potential at large Galactocentric distances. In this work I explore the impact of these extra data on the ability to fit the potential using the method of action clustering, which statistically maximizes the information content (clumpiness) of the action space of tidal streams, eliminating the need to determine stream membership for individual stars. Using a mock halo in a toy spherical potential, updated post-launch error models for Gaia, and estimates for RV and distance errors for the tracers to be followed up, I show that combining either form of additional information with the Gaia catalog greatly reduces the bias in determining the scale radius and total mass of the Galaxy, compared to the use of Gaia data alone.
High surface density, rapidly star-forming galaxies are observed to have $\approx 50-100\,{\rm km\,s^{-1}}$ line-of-sight velocity dispersions, which are much higher than expected from supernova driving alone, but may arise from large-scale gravitational instabilities. Using three-dimensional simulations of local regions of the interstellar medium, we explore the impact of high velocity dispersions that arise from these disk instabilities. Parametrizing disks by their surface densities and epicyclic frequencies, we conduct a series of simulations that probe a broad range of conditions. Turbulence is driven purely horizontally and on large scales, neglecting any energy input from supernovae. We find that such motions lead to strong global outflows in the highly-compact disks that were common at high redshifts, but weak or negligible mass loss in the more diffuse disks that are prevalent today. Substantial outflows are generated if the one-dimensional horizontal velocity dispersion exceeds $\approx 35\,{\rm km\,s^{-1}},$ as occurs in the dense disks that have star formation rate densities above $\approx 0.1\,{\rm M}_\odot\,{\rm yr}^{-1}\,{\rm kpc}^{-2}.$ These outflows are triggered by a thermal runaway, arising from the inefficient cooling of hot material coupled with successive heating from turbulent driving. Thus, even in the absence of stellar feedback, a critical value of the star-formation rate density for outflow generation can arise due to a turbulent heating instability. This suggests that in strongly self-gravitating disks, outflows may be enhanced by, but need not caused by, energy input from supernovae.
We exploit ALMA 870um observations to measure the star-formation rates (SFRs) of eight X-ray detected Active Galactic Nuclei (AGNs) in a z~3.1 protocluster, four of which reside in extended Ly-alpha haloes (often termed Ly-alpha blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of ~220-410~M_sun/yr; the non detection of the other five AGNs places SFR upper limits of <210 M_sun/y. The mean SFR of the protocluster AGNs (~110-210 M_sun/yr) is consistent (within a factor of ~0.7-2.3) with that found for co-eval AGNs in the field, implying that galaxy growth is not significantly accelerated across the protocluster environment. However, when also considering ALMA data from the literature, we find some evidence for significantly elevated mean SFRs (up-to a factor of ~4.3 over the field) for the AGNs at the protocluster core. We also show that all of the four protocluster LABs are associated with an ALMA counterpart within the extent of their Ly-alpha emission. The SFRs of the ALMA sources within the LABs (~150-410 M_sun/yr) are consistent with those expected for co-eval massive star-forming galaxies in the field. Furthermore, the two giant LABs (with physical extents of >100 kpc) do not host more luminous star formation than the smaller LABs, despite being an order of magnitude brighter in Ly-alpha emission. We use these results to discuss star formation as the power source of LABs.
We survey 44 young stellar objects located near the edges of mid-IR-identified bubbles in CS (1-0) using the Green Bank Telescope. We detect emission in 18 sources, indicating young protostars that are good candidates for being triggered by the expansion of the bubble. We calculate CS column densities and abundances. Three sources show evidence of infall through non-Gaussian line-shapes. Two of these sources are associated with dark clouds and are promising candidates for further exploration of potential triggered star formation. We obtained on-the-fly maps in CS (1-0) of three sources, showing evidence of significant interactions between the sources and the surrounding environment.
Emission from carbon monoxide (CO) is ubiquitously used as a tracer of dense star forming molecular clouds. There is, however, growing evidence that a significant fraction of CO emission originates from diffuse molecular gas. Quantifying the contribution of diffuse CO-emitting gas is vital for understanding the relation between molecular gas and star formation. We examine the Galactic distribution of two CO-emitting gas components, a high column density component detected in 13CO and 12CO, and a low column density component detected in 12CO, but not in 13CO. The "diffuse" and "dense" components are identified using a combination of smoothing, masking, and erosion/dilation procedures, making use of three large-scale 12CO and 13CO surveys of the Inner and Outer Milky Way. The diffuse component, which globally represents 25 (1.5x1e8 Mo) of the total molecular gas mass (6.5x1e8 Mo), is more extended perpendicular to the Galactic plane. The fraction of diffuse gas increases from 15% at a galactocentric radius of 3 kpc to 50% at 15 kpc, and increases with decreasing surface density. In the Inner Galaxy, a yet denser component traced by CS emission represents 14% of the total molecular gas mass traced by 12CO emission. Only 14% of the molecular gas mass traced by 12CO emission is identified as part of molecular clouds in 12CO surveys by cloud identification algorithms. This study indicates that CO emission not only traces star forming clouds, but also a significant diffuse molecular ISM component.
The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2 deg$^2$ of the COSMOS field with an effective exposure of $\simeq$160 ks over the central 1.5 deg$^2$ and of $\simeq$80 ks in the remaining area. The survey is the combination of 56 new observations, obtained as an X-ray Visionary Project, with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2$\times 10^{-5}$. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft and hard band). The limiting depths are 2.2 $\times$ 10$^{-16}$, 1.5 $\times$ 10$^{-15}$ and 8.9$\times$ 10$^{-16}$ ${\rm erg~cm}^{-2}~{\rm s}^{-1}$ in the 0.5-2, 2-10 and 0.5-10 keV bands, respectively. The observed fraction of obscured AGN with column density $> 10^{22}$ cm$^{-2}$ from the hardness ratio (HR) is $\sim$50$^{+17}_{-16}$%. Given the large sample, we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5-10%. For the first time, we compute number counts for obscured (HR$>$-0.2) and unobscured (HR$<$-0.2) sources and find significant differences between the two populations in the soft band. Due to the un-precedent large exposure, COSMOS-Legacy area is 3 times larger than surveys at similar depth and its depth is 3 times fainter than surveys covering similar area. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.
We present a detailed statistical analysis of possible non-linearities in the Period-Luminosity (P-L), Period-Wesenheit (P-W) and Period-Color (P-C) relations for Cepheid variables in the LMC at optical ($VI$) and near-infrared ($JHK_{s}$) wavelengths. We test for the presence of possible non-linearities and determine their statistical significance by applying a variety of robust statistical tests ($F$-test, Random-Walk, Testimator and the Davies test) to optical data from OGLE III and near-infrared data from LMCNISS. For fundamental-mode Cepheids, we find that the optical P-L, P-W and P-C relations are non-linear at 10 days. The near-infrared P-L and the $W^H_{V,I}$ relations are non-linear around 18 days; this break is attributed to a distinct variation in mean Fourier amplitude parameters near this period for longer wavelengths as compared to optical bands. The near-infrared P-W relations are also non-linear except for the $W_{H,K_s}$ relation. For first-overtone mode Cepheids, a significant change in the slope of P-L, P-W and P-C relations is found around 2.5 days only at optical wavelengths. We determine a global slope of $\textrm{-}3.212\pm0.013$ for the $W^H_{V,I}$ relation by combining our LMC data with observations of Cepheids in Supernovae host galaxies \citep{riess11}. We find this slope to be consistent with the corresponding LMC relation at short periods, and significantly different to the long-period value. We do not find any significant difference in the slope of the global-fit solution using a linear or non-linear LMC P-L relation as calibrator, but the linear version provides a $2\times$ better constraint on the slope and metallicity coefficient.
While recent observations provide evidence that super-Chandrasekhar Type Ia supernovae and at least a fraction of normal Type Ia supernovae probably originate from double-degenerate systems, these two subclasses show distinct characteristics observationally. Here we report an intermediate supernova iPTF13asv that may bridge this gap. On the one hand, similar to normal Type Ia supernovae, the over-luminous iPTF13asv follows the empirical relation between the peak magnitude, the lightcurve shape and its intrinsic color, and shows a near-IR secondary maximum like normal supernovae. On the other hand, similar to super-Chandrasekhar events, it has strong UV emission around maximum, low expansion velocities and persistent carbon absorption. We estimate a $^{56}$Ni mass of $0.81^{+0.10}_{-0.18}M_\odot$ and a total ejecta mass of $1.44^{+0.44}_{-0.12}M_\odot$. Despite these similarities, iPTF13asv lacks iron absorption in its early-phase spectra, indicating a stratified ejecta structure with weak mixing. Based on the strong stratification of the ejecta and the similarity to super-Chandrasekhar events, we infer that iPTF13asv probably originates from a double-degenerate system.
We present a multiplicity study of all known protostars (94) in the Perseus molecular cloud from a Karl G. Jansky Very Large Array (VLA) survey at Ka-band (8 mm and 1 cm) and C-band (4 cm and 6.6 cm). The observed sample has a bolometric luminosity range between 0.1 L$_{\odot}$ and $\sim$33 L$_{\odot}$, with a median of 0.7 L$_{\odot}$. This multiplicity study is based on the Ka-band data, having a best resolution of $\sim$0.065" (15 AU) and separations out to $\sim$43" (10000 AU) can be probed. The overall multiplicity fraction (MF) is found to be of 0.40$\pm$0.06 and the companion star fraction (CSF) is 0.71$\pm$0.06. The MF and CSF of the Class 0 protostars are 0.57$\pm$0.09 and 1.2$\pm$0.2, and the MF and CSF of Class I protostars are both 0.23$\pm$0.08. The distribution of companion separations appears bi-modal, with a peak at $\sim$75 AU and another peak at $\sim$3000 AU. Turbulent fragmentation is likely the dominant mechanism on $>$1000 AU scales and disk fragmentation is likely to be the dominant mechanism on $<$200 AU scales. Toward three Class 0 sources we find companions separated by $<$30 AU. These systems have the smallest separations of currently known Class 0 protostellar binary systems. Moreover, these close systems are embedded within larger (50 AU to 400 AU) structures and may be candidates for ongoing disk fragmentation.
Links to: arXiv, form interface, find, astro-ph, recent, 1601, contact, help (Access key information)
We have selected a sample of extremely isolated galaxies (EIGs) from the
local Universe ($\mbox{z} < 0.024$), using a simple isolation criterion: having
no known neighbours closer than $300\,{\rm km\,s}^{-1}$
($3\,h^{-1}\,\mbox{Mpc}$) in the three-dimensional redshift space
$(\alpha,\delta,\mbox{z})$. The sample is unique both in its level of isolation
and in the fact that it utilizes HI redshifts from the Arecibo Legacy Fast ALFA
survey (ALFALFA).
We analysed the EIG sample using cosmological simulations and found that it
contains extremely isolated galaxies with normal mass haloes which have evolved
gradually with little or no "major events" (major mergers, or major mass-loss
events) in the last $3\,\mbox{Gyr}$. The fraction of EIGs which deviate from
this definition (false positives) is 5%-10%.
For the general population of dark matter haloes it was further found that
the mass accretion (relative to the current halo mass) is affected by the halo
environment mainly through strong interactions with its neighbours. As long as
a halo does not experience major events, its Mass Accretion History (MAH) does
not depend significantly on its environment. "Major events" seem to be the main
mechanism that creates low-mass subhaloes ($M_{halo} <
10^{10}\,h^{-1}\,M_\odot$) that host galaxies (with $\mbox{M}_{g} \lesssim
-14$).
We use the NIHAO galaxy formation simulations to make predictions for the baryonic budget in present day galaxies ranging from dwarf to Milky Way masses. The sample is made of 88 independent high resolution cosmological zoom-in simulations. NIHAO galaxies reproduce key properties of observed galaxies, such as the stellar mass vs halo mass and cold gas vs stellar mass relations. Thus they make plausible predictions for the baryon budget. We present the mass fractions of stars, cold gas, cool gas, warm-hot gas, and hot gas inside the virial radius. Compared to the predicted baryon mass, using the dark halo mass and the universal baryon fraction, we find that for all of our haloes, the missing mass is not just outside the virial radius, it has been relocated past 2 virial radius. Haloes of dwarf mass are missing ~ 90% of their baryons. More massive haloes (Milky Way mass) retain a higher fraction of their baryons, with ~ 30% missing, consistent with observational estimates.
We study the properties of HI gas in the outer regions (~2r_25) of a spiral galaxy, UGC 00439 (z = 0.01769), using HI 21-cm absorption towards different components of an extended background radio source, J0041$-$0043 (z = 1.679). The radio source exhibits a compact core coincident with the optical quasar and two lobes separated by ~7 kpc, all at an impact parameter ~25 kpc. The HI 21-cm absorption detected towards the southern lobe is found to extend over ~2 kpc^2. The absorbing gas shows sub-kpc-scale structures with the line-of-sight velocities dominated by turbulent motions. Much larger optical depth variations over 4-7 kpc-scale are revealed by the non-detection of HI 21-cm absorption towards the radio core and the northern lobe, and the detection of NaI and CaII absorption towards the quasar. This could reflect a patchy distribution of cold gas in the extended HI disc. We also detect HI 21-cm emission from UGC 00439 and two other galaxies within ~150 kpc to it, that probably form an interacting group. However, no HI 21-cm emission from the absorbing gas is detected. Assuming a linear extent of ~4 kpc, as required to cover both the core and the southern lobe, we constrain the spin temperature <~300 K for the absorbing gas. The kinematics of the gas and the lack of signatures of any ongoing in situ star formation are consistent with the absorbing gas being at the kinematical minor axis and corotating with the galaxy. Deeper HI 21-cm observations would help to map in greater detail both the large- and small-scale structures in the HI gas associated with UGC 00439.
We investigate the correlations between the black hole mass $M_{BH}$, the velocity dispersion $\sigma$, the bulge mass $M_{Bu}$, the bulge average spherical density $\rho_h$ and its spherical half mass radius $r_h$, constructing a database of 97 galaxies (31 core ellipticals, 17 power-law ellipticals, 30 classical bulges, 19 pseudo bulges) by joining 72 galaxies from the literature to 25 galaxies observed during our recent SINFONI black hole survey. For the first time we discuss the full error covariance matrix. We analyse the well known \msig\ and \mbu\ relations and establish the existence of statistically significant correlations between $M_{Bu}$ and $r_h$ and anti-correlations between $M_{Bu}$ and $\rho_h$. We establish five significant bivariate correlations (\msigrho, \msigr, \mbus, \mburho, \mbur) that predict $M_{BH}$ of 77 core and power-law ellipticals and classical bulges with measured and intrinsic scatter as small as $\approx 0.36$ dex and $\approx 0.33$ dex respectively, or 0.26 dex when the subsample of 45 galaxies defined by \citet{KormendyHo2013} is considered. In contrast, pseudo bulges have systematically lower $M_{BH}$, but approach the predictions of all the above relations at spherical densities $\rho_h\ge 10^{10} M_\odot/kpc^3$ or scale lengths $r_h\le 1$ kpc. These findings fit in a scenario of co-evolution of BH and classical-bulge masses, where core ellipticals are the product of dry mergers of power-law bulges and power-law Es and bulges the result of (early) gas-rich mergers and of disk galaxies. In contrast, the (secular) growth of BHs is decoupled from the growth of their pseudo bulge hosts, except when (gas) densities are high enough to trigger the feedback mechanism responsible for the existence of the correlations between $M_{BH}$ and galaxy structural parameters.
We use cosmological hydrodynamical simulations of the APOSTLE project to examine the fraction of baryons in $\Lambda$CDM haloes that collect into galaxies. This `galaxy formation efficiency' correlates strongly and with little scatter with halo mass, dropping steadily towards dwarf galaxies. The baryonic mass of a galaxy may thus be used to place a lower limit on total halo mass and, consequently, on its asymptotic maximum circular velocity. A number of dwarfs seem to violate this constraint, having baryonic masses up to ten times higher than expected from their rotation speeds, or, alternatively, rotating at only half the speed expected for their mass. Taking the data at face value, either these systems have formed galaxies with extraordinary efficiency - highly unlikely given their shallow potential wells - or they inhabit haloes with extreme deficits in their dark matter content. This `missing dark matter' is reminiscent of the inner mass deficits of galaxies with slowly-rising rotation curves, but extends to regions larger than the luminous galaxies themselves, disfavouring explanations based on star formation-induced `cores' in the dark matter. An alternative could be that galaxy inclination errors have been underestimated, and that these are just systems where inferred mass profiles have been compromised by systematic uncertainties in interpreting the velocity field. This should be investigated further, since it might provide a simple explanation not only for missing-dark-matter galaxies but also for other challenges to our understanding of the inner structure of cold dark matter haloes.
We present an interferometric survey of the 44 GHz class I methanol maser transition toward a sample of 69 sources consisting of High Mass Protostellar Object candidates and Ultracompact (UC) H II regions. We found a 38% detection rate (16 of 42) in the HMPO candidates and a 54% detection rate (13 of 24) for the regions with ionized gas. This result indicates that class I methanol maser emission is more common toward more evolved young stellar objects of our sample. Comparing with similar interferometric data sets, our observations show narrower linewidths, likely due to our higher spatial resolution. Based on a comparison between molecular outflow tracers and the maser positions, we find several cases where the masers appear to be located at the outflow interface with the surrounding core. Unlike previous surveys, we also find several cases where the masers appear to be located close to the base of the molecular outflow, although we can not discard projection effects. This and other surveys of class I methanol masers not only suggest that these masers may trace shocks at different stages, but may even trace shocks arising from a number of different phenomena occurring in star-forming regions: young/old outflows, cloud-cloud collisions, expanding H II regions, among others.
The physical mechanisms that induce the transformation of a certain mass of gas in new stars are far from being well understood. Infrared bubbles associated with HII regions have been considered to be a good sample to investigate triggered star formation. In this paper we report on the investigation of the dust properties of the infrared bubble N4 around the HII region G11.898+0.747, analyzing its interaction with the surroundings and star formation histories therein, aiming at determining the possibility of star formation triggered by the expansion of the bubble. Using Herschel PACS and SPIRE images with a wide wavelength coverage, we reveal the dust properties over the entire bubble. Meanwhile, we are able to identify six dust clumps surrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K, mean column density of 1.7 $\times10^{22}$ cm$^{-2}$, mean volume density of about 4.4 $\times10^{4}$ cm$^{-3}$, and a mean mass of 320 $M_{\odot}$. In addition, from PAH emission seen at 8 $\mu$m, free-free emission detected at 20 cm and a probability density function in special regions, we could identify clear signatures of the influence of the HII region on the surroundings. There are hints of star formation, though further investigation is required to demonstrate that N4 is the triggering source.
(doctoral thesis of Michal Bilek, finished on June 19, 2015)
MOND is an observational rule for predicting the acceleration of stars and
galaxies from the distribution of the visible matter. It possibly stems from a
new law of physics. I list the theoretical aspects of MOND, its achievements
and problems. MOND has been tested mainly in disc galaxies so far. Its tests in
elliptical galaxies are rare because the MOND effects are small for them in the
parts observable by the conventional methods. In the thesis, I explain the
methods and ideas I developed for testing MOND in the ellipticals using stellar
shells. Moreover, the shells enable us to test MOND for stars in radial orbits
for the first time. The shells are results of galactic interactions. I discuss
the shell formation mechanisms and summarize the findings from shell
observations and simulations.
The thesis contains as yet unpublished results mainly in: 1) the introduction
of Sect. 3 (the expected differences in the shell morphology in the Newtonian
dynamics with dark matter and in MOND), and 2) Sect. 2.4.1 (formulas for
modeling the evolution of shell radii).
We present a novel technique for ranking the relative importance of galaxy properties in the process of quenching star formation. Specifically, we develop an artificial neural network (ANN) approach for pattern recognition and apply it to a population of over 400,000 central galaxies taken from the Sloan Digital Sky Survey Data Release 7. We utilise a variety of physical galaxy properties for training the pattern recognition algorithm to recognise star forming and passive systems, for a `training set' of $\sim$100,000 galaxies. We then apply the ANN model to a `verification set' of $\sim$100,000 different galaxies, randomly chosen from the remaining sample. The success rate of each parameter singly, and in conjunction with other parameters, is taken as an indication of how important the parameters are to the process(es) of central galaxy quenching. We find that central velocity dispersion, bulge mass and B/T are excellent predictors of the passive state of the system, indicating that properties related to the central mass of the galaxy are most closely linked to the cessation of star formation. Larger scale galaxy properties (total or disk stellar masses), or those linked to environment (halo masses or $\delta_5$) perform significantly less well. Our results are plausibly explained by AGN feedback driving the quenching of central galaxies, although we discuss other possibilities as well.
The distribution of young open clusters in the Galactic plane within 3 kpc from the Sun suggests the existence of the outer ring R1R2' in the Galaxy. The optimum value of the solar position angle with respect to the major axis of the bar, theta_b, providing the best agreement between the distribution of open clusters and model particles is theta_b=35 +/- 10 degrees. The kinematical features obtained for young open clusters and OB-associations with negative Galactocentric radial velocity VR indicate the solar location near the descending segment of the outer ring R2.
The main goal of Galactic Archaeology is understanding the formation and evolution of the basic Galactic components. This requires sophisticated chemo-dynamical modeling, where disc asymmetries (e.g., perturbations from the central bar, spirals arms, and infalling satellites) and non-equilibrium processes are taken into account self-consistently. Here we discuss the current status of Galactic chemo-dynamical modeling and focus on a recent hybrid technique, which helps circumvent traditional problems with chemical enrichment and star formation encountered in fully self-consistent cosmological simulations. We show that this model can account for a number of chemo-kinematic relations in the Milky Way. In addition, we demonstrate that (1) our model matches well the observed age-[alpha/Fe] and age-[Fe/H] relations and (2) that the scatter in the age-[Fe/H] relation cannot be simply explained by blurring (stars on apo- and pericenters visiting the solar vicinity) but significant radial migration (stars born elsewhere but ending up at the solar vicinity today because of a change in guiding radius) is needed. We emphasize the importance of accurate stellar ages, such as those obtained through asteroseismology by the CoRoT and Kepler missions, for breaking the degeneracy among different Galactic evolution scenarios.
CEMP-$r/s$ stars are metal-poor stars with enhanced abundances of carbon and heavy elements associated with the slow ($s$-) and rapid ($r$-) neutron-capture process. It is believed that carbon and $s$-elements were accreted from the wind of an AGB primary star, a scenario that is generally accepted to explain the formation of CEMP stars that are only enhanced in $s$-elements (CEMP-$s$ stars). The origin of $r$-element-enrichment in CEMP-$r/s$ stars is debated and many formation scenarios have been put forward. We aim to determine the likelihood of the scenarios proposed to explain the formation of CEMP-$r/s$ stars. We calculate the frequency of CEMP-$r/s$ stars among CEMP-$s$ stars for a variety of scenarios, and we compare it with that determined from an observed sample of CEMP-$r/s$ stars collected from the literature. The theoretical frequency of CEMP-$r/s$ stars predicted in most scenarios underestimates the observed ratio by at least a factor of 5. If the enrichments in $s$- and $r$-elements are independent, the model ratio of CEMP-$r/s$ to CEMP-$s$ stars is about 22%, that is approximately consistent with the lowest estimate of the observed ratio. However, this model predicts that about one third of all carbon-normal stars have [Ba/Fe] and [Eu/Fe] higher than 1, and that 40% of all CEMP stars have [Ba/Eu]$\le0$. Stars with these properties are at least ten times rarer in our observed sample. The $intermediate$ or $i$-process, which is supposedly active in some circumstances during the AGB phase, could provide an explanation of the origin of CEMP-$r/s$ stars, similar to that of CEMP-$s$ stars, in the context of wind mass accretion in binary systems. Further calculations of the nucleosynthesis of the $i$-process and of the detailed evolution of late AGB stars are needed to investigate if this scenario predicts a CEMP-$r/s$ star frequency consistent with the observations.
Using our mathematical framework developed in \cite{cresson-pierret_scale} called \emph{scale dynamics}, we propose in this paper a new way of interpreting the problem of adding or modifying potentials in mechanics and specifically in galactic dynamics. An application is done for the two-body problem with a Keplerian potential showing that the velocity of the orbiting body is constant. This would explain the observed phenomenon in the flat rotation curves of galaxies without adding \emph{dark matter} or modifying Newton's law of dynamics.
The AKARI Deep Field South (ADF-S) is a large extragalactic survey field that is covered by multiple instruments, from optical to far-IR and radio. I summarise recent results in this and related fields prompted by the release of the Herschel far-IR/submm images, including studies of cold dust in nearby galaxies, the identification of strongly lensed distant galaxies, and the use of colour selection to find candidate very high redshift sources. I conclude that the potential for significant new results from the ADF-S is very great. The addition of new wavelength bands in the future, eg. from Euclid, SKA, ALMA and elsewhere, will boost the importance of this field still further.
Throughout the last decade sensitive infrared observations obtained by the Spitzer Space Telescope significantly increased the known population of YSOs associated with nearby molecular clouds. With such a census recent studies have characterized pre-main sequence stars (PMS) and determined parame- ters from different wavelengths. Given the restricted Spitzer coverage of some of these clouds, relative to their extended regions, these YSO populations may represent a limited view of star formation in these regions. We are taking advantage of mid-infrared observations from the NASA Wide Field Infrared Survey Explorer (WISE), which provides an all sky view and therefore full coverage of the nearby clouds, to assess the degree to which their currently known YSO population may be representative of a more complete population. We extend the well established classification method of the Spitzer Legacy teams to archived WISE observations. We have adopted 2MASS photometry as a standard catalogue for comparisons. Besides the massive embedded cluster IC5146 we provide a multiband view of five new embedded clusters in its surroundings that we discovered with WISE. In short, the analysis in- volves the following for the presently studied cluster sample: (1) extraction of 2MASS/WISE/Spitzer photometry in a wide circular region; (2) field-star decontamination to enhance the intrinsic Colour-magnitude diagram (CMD) morphology (essential for a proper derivation of reddening, age, and distance from the Sun); and (3) construction of Colour-magnitude filters, for more contrasted stellar radial density profiles (RDPs).
Links to: arXiv, form interface, find, astro-ph, recent, 1601, contact, help (Access key information)
A correlation between the 24 {\mu}m continuum and the [NII] 205 {\mu}m line emission may arise if both quantities trace the star formation activity on spatially-resolved scales within a galaxy, yet has so far only been observed in the nearby edge-on spiral galaxy NGC 891. We therefore assess whether the [NII] 205 - 24 {\mu}m emission correlation has some physical origin or is merely an artefact of line-of-sight projection effects in an edge-on disc. We search for the presence of a correlation in Herschel and Spitzer observations of two nearby face-on galaxies, M51 and M83, and the interacting Antennae galaxies NGC 4038 and 4039. We show that not only is this empirical relationship also observed in face-on galaxies, but also that the correlation appears to be governed by the star formation rate (SFR). Both the nuclear starburst in M83 and the merger-induced star formation in NGC 4038/9 exhibit less [NII] emission per unit SFR surface density than the normal star-forming discs. These regions of intense star formation exhibit stronger ionization parameters, as traced by the 70/160 {\mu}m far-infrared colour, that suggest the presence of higher ionization lines that may become more important for gas cooling, thereby reducing the observed [NII] 205 {\mu}m line emission in regions with higher star formation rates. Finally, we present a general relation between the [NII] 205 {\mu}m line flux density and SFR density for normal star-forming galaxies, yet note that future studies should extend this analysis by including observations with wider spatial coverage for a larger sample of galaxies.
Following a number of conflicting studies of M87's mass profile, we undertake a dynamical analysis of multiple tracer populations to constrain its mass over a large radius range. We combine stellar kinematics in the central regions with the dynamics of 612 globular clusters out to 200 kpc and satellite galaxies extending to scales comparable with the virial radius. Using a spherical Jeans analysis, we are able to disentangle the mass contributions from the dark and baryonic components and set constraints on the structure of each. Assuming isotropy, we explore four different models for the dark matter halo and find that a centrally-cored dark matter distribution is preferred. We infer a stellar mass-to-light ratio $\Upsilon_{\star,v} = 6.9 \pm 0.1$ -- consistent with a Salpeter-like IMF -- and a core radius $r_c = 67 \pm 20$ kpc. We then introduce anisotropy and find that, while the halo remains clearly cored, the radial stellar anisotropy has a strong impact on both $\Upsilon_{\star,v}$ and the core's radius; here we find $\Upsilon_{\star,v} = 3.50_{-0.36}^{+0.32}$ -- consistent with a Chabrier-like IMF -- and $r_c = 19.00_{-8.34}^{+8.38}$ kpc. Thus the presence of a core at the centre of the dark halo is robust against anisotropy assumptions, while the stellar mass and core size are not. We are able to reconcile previously discrepant studies by showing that modelling the globular cluster data alone leads to the very different inference of a super-NFW cusp, thus highlighting the value of multiple-population modelling, and we point to the possible role of M87's AGN and the cluster environment in forming the central dark matter core.
Energetic feedback due to active galactic nuclei (AGN) is likely to play an important role in the observed anti-hierarchical trend in the evolution of galaxies, and yet the energy injected into the circumgalactic medium by this process is largely unknown. One promising approach to constrain this feedback is through measurements of CMB spectral distortions due to the thermal Sunyaev-Zel'dovich (tSZ) effect, whose magnitude is directly proportional to the energy input by AGN. Here we co-add South Pole Telescope SZ (SPT-SZ) survey data around a large set of massive quiescent elliptical galaxies at z >= 0.5. We use data from the Blanco Cosmology Survey and VISTA Hemisphere Survey to create a large catalog of galaxies split up into two redshift bins, with 3394 galaxies at 0.5 <= z <= 1.0 and 924 galaxies at 1.0 <= z <= 1.5, with typical stellar masses of 1.5 x 10^11 M_Sun. We then co-add the emission around these galaxies, resulting in a measured tSZ signal at 2.2 sigma significance for the lower redshift bin and a contaminating signal at 1.1 sigma for the higher redshift bin. To remove contamination due to dust emission, we use SPT-SZ source counts to model a contaminant source population in both the SPT-SZ bands and Planck high-frequency bands for a subset of 937 low-redshift galaxies and 240 high-redshift galaxies. This increases our detection to 3.6 sigma for low redshifts and 0.9 sigma for high redshifts. We find the mean angularly-integrated Compton-y values to be 2.2 (-0.7+0.9) x 10^-7 Mpc^2 for low redshifts and 1.7 (-1.8+2.2) x 10^-7 Mpc^2 for high redshifts, corresponding to total thermal energies of 7.6 (-2.3+3.0) x 10^60 ergs and 6.0 (-6.3+7.7) x 10^60 ergs, respectively. These numbers are higher than expected from simple theoretical models that do not include AGN feedback, and serve as constraints that can be applied to current simulations of massive galaxy formation. (abridged)
This Letter presents a new, remarkably simple diagnostic specifically designed to derive chemical abundances for high redshift galaxies. It uses only the H \alpha, [N II] and [S II] emission lines, which can usually be observed in a single gating stetting, and is almost linear up to an abundance of 12+log (O/H) = 9.05. It can be used over the full abundance range encountered in high redshift galaxies. By its use of emission lines located close together in wavelength, it is also independent of reddening. Our diagnostic depends critically on the calibration of the N/O ratio. However, by using realistic stellar atmospheres combined with the N/O vs. O/H abundance calibration derived locally from stars and H II regions, and allowing for the fact that high-redshift H II regions have both high ionisation parameters \emph{and} high gas pressures, we find that the observations of high-redshift galaxies can be simply explained by the models without having to invoke arbitrary changes in N/O ratio, or the presence of unusual quantities of Wolf-Rayet stars in these galaxies.
Recent high-quality observations of dwarf and low surface brightness (LSB) galaxies have shown that their dark matter (DM) halos prefer flat central density profiles. On the other hand the standard cold dark matter model simulations predict a more cuspy behavior. Feedback from star formation has been widely used to reconcile simulations with observations, this might be successful in field dwarf galaxies but its success in low mass galaxies remains uncertain. One model that have received much attention is the scalar field dark matter model. Here the dark matter is a self-interacting ultra light scalar field that forms a cosmological Bose-Einstein condensate, a mass of $10^{-22}$eV/c$^2$ is consistent with flat density profiles in the centers of dwarf spheroidal galaxies, reduces the abundance of small halos, might account for the rotation curves even to large radii in spiral galaxies and has an early galaxy formation. The next generation of telescopes will provide better constraints to the model that will help to distinguish this particular alternative to the standard model of cosmology shedding light into the nature of the mysterious dark matter.
Broad emission lines in active galactic nuclei (AGNs) mainly arise from gas photoionized by continuum radiation from an accretion disk around a central black hole. The shape of the broad-line profile, described by ${\cal D}_{_{\rm H\beta}}={\rm FWHM}/\sigma_{_{\rm H\beta}}$, the ratio of full width at half maximum to the dispersion of broad H$\beta$, reflects the dynamics of the broad-line region (BLR) and correlates with the dimensionless accretion rate ($\dot{\mathscr{M}}$) or Eddington ratio ($L_{\rm bol}/L_{\rm Edd}$). At the same time, $\dot{\mathscr{M}}$ and $L_{\rm bol}/L_{\rm Edd}$ correlate with ${\cal R}_{\rm Fe}$, the ratio of optical Fe II to H$\beta$ line flux emission. Assembling all AGNs with reverberation mapping measurements of broad H$\beta$, both from the literature and from new observations reported here, we find a strong bivariate correlation of the form $\log(\dot{\mathscr{M}},L_{\rm bol}/L_{\rm Edd})=\alpha+\beta{\cal D}_{_{\rm H\beta}}+\gamma{\cal R}_{\rm Fe},$ where $\alpha=(2.47,0.31)$, $\beta=-(1.59,0.82)$ and $\gamma=(1.34,0.80)$. We refer to this as the fundamental plane of the BLR. We apply the plane to a sample of $z < 0.8$ quasars to demonstrate the prevalence of super-Eddington accreting AGNs are quite common at low redshifts.
In this paper, we present the measurements of the [NII] 205micron line ([NII]205) for a flux-limited sample of 122 (ultra-)luminous infrared galaxies [(U)LIRGs] and 20 additional normal galaxies, obtained with the Herschel Space Observatory. We explore the far-infrared (FIR) color dependence of the [NII]205 (L[NII]205) to the total infrared (LIR) luminosity ratio, and find that L[NII]205/LIR only depends modestly on the 70-to-160 micron flux density ratio (f70/f160) when f70/f160 <~ 0.6, whereas such dependence becomes much steeper for f70/f160> 0.6. We also investigate the relation between L[NII]205 and star formation rate (SFR), and show that L[NII]205 has a nearly linear correlation with SFR, albeit the intercept of such relation varies somewhat with f60/f100, consistent with our previous conclusion that \NIIab\ emission can serve as a SFR indicator with an accuracy of ~0.4 dex, or ~0.2 dex if f60/f100 is known independently. Furthermore, together with the ISO measurements of [NII] 122 micron emission we use a total of ~200 galaxies to derive the local [NII]205 luminosity function (LF) by tying it to the known IR LF with a bivariate method. As a practical application, we also compute the local SFR volume density ($\dot{\rho}_{\rm SFR}$) using the newly derived SFR calibrator and LF. The resulting $\log\,\dot{\rho}_{\rm SFR} = -1.96\pm0.11$ $M_\odot$\,yr$^{-1}$\,Mpc$^{-3}$ agrees well with previous studies. Finally, we determine the electron densities ($n_e$) of the ionized medium for a subsample of 12 (U)LIRGs with both [NII]205 and [NII]122 data, and find that $n_e$ is in the range of ~1-100 cm$^{-3}$, with a median value of 22 cm$^{-3}$
A new mechanism is described, analyzed and visualized, for the dissipation of
suprathermal rotation energy of molecules in magnetic fields, a necessary
condition for their alignment. It relies upon the Lorentz force perturbing the
motion of every atom of the structure, as each is known to carry its own net
electric charge because of spatial fluctuations in electron density. If the
molecule is large enough that the frequency of its lowest-frequency phonon lies
near or below the rotation frequency, then the rotation couples with the
molecular normal modes and energy flows from the former to the latter. The rate
of this exchange is very fast, and the vibrational energy is radiated away in
the IR at a still faster rate, which completes the removal of rotation energy.
The energy decay rate scales like the field intensity, the initial angular
velocity, the number of atoms in the grain and the inverse of the moment of
inertia. It does not depend on the susceptibility. Here, the focus is on
carbon-rich molecules which are diamagnetic. The same process must occur if the
molecule is paramagnetic or bathes in an electric field instead.
A semi-empirical method of chemical modeling was used extensively to
illustrate and quantify these concepts as applied to a hydrocarbon molecule.
The motion of a rotating molecule in a field was monitored in time so as to
reveal the energy transfer and visualize the evolution of its orientation
towards the stable configuration.
We examine deep Chandra X-ray observations of the Centaurus cluster of galaxies, Abell 3526. Applying a gradient magnitude filter reveals a wealth of structure, from filamentary soft emission on 100pc (0.5 arcsec) scales close to the nucleus to features 10s of kpc in size at larger radii. The cluster contains multiple high-metallicity regions with sharp edges. Relative to an azimuthal average, the deviations of metallicity and surface brightness are correlated, and the temperature is inversely correlated, as expected if the larger scale asymmetries in the cluster are dominated by sloshing motions. Around the western cold front are a series of ~7 kpc 'notches', suggestive of Kelvin-Helmholtz instabilities. The cold front width varies from 4 kpc down to close to the electron mean free path. Inside the front are multiple metallicity blobs on scales of 5-10 kpc, which could have been uplifted by AGN activity, also explaining the central metallicity drop and flat inner metallicity profile. Close to the nucleus are multiple shocks, including a 1.9-kpc-radius inner shell-like structure and a weak 1.1-1.4 Mach number shock around the central cavities. Within a 10 kpc radius are 9 depressions in surface brightness, several of which appear to be associated with radio emission. The shocks and cavities imply that the nucleus has been repeatedly active on 5-10 Myr timescales, indicating a tight balance between heating and cooling. We confirm the presence of a series of linear quasi-periodic structures. If they are sound waves, the ~5 kpc spacing implies a period of 6 Myr, similar to the ages of the shocks and cavities. Alternatively, these structures may be Kelvin-Helmholtz instabilities, their associated turbulence or amplified magnetic field layers.
In the present work we used a grid of photoionization models combined with stellar population synthesis models to derive reliable Ionization Correction Factors (ICFs) for the sulphur in star-forming regions. These models cover a large range of nebular parameters and yielding ionic abundances in consonance with those derived through optical and infrared observational data of star-forming regions. From our theoretical ICFs, we suggested an {\alpha} value of 3.27 in the classical Stasinska formulae. We compared the total sulphur abundance in the gas phase of a large sample of objects by using our Theoretical ICF and other approaches. In average, the differences between the determinations via the use of the different ICFs considered are similar to the uncertainties in the S/H estimations. Nevertheless, we noted that for some objects it could reach up to about 0.3 dex for the low metallicity regime. Despite of the large scatter of the points, we found a trend of S/O ratio to decrease with the metallicity, independently of the ICF used to compute the sulphur total abundance.
We measured the gas abundance profiles in a sample of 122 face-on spiral galaxies observed by the CALIFA survey and included all spaxels whose line emission was consistent with star formation. This type of analysis allowed us to improve the statistics with respect to previous studies, and to properly estimate the oxygen distribution across the entire disc to a distance of up to 3-4 disc effective radii (r$_e$). We confirm the results obtained from classical HII region analysis. In addition to the general negative gradient, an outer flattening can be observed in the oxygen abundance radial profile. An inner drop is also found in some cases. There is a common abundance gradient between 0.5 and 2.0 r$_e$ of $\alpha_{O/H} = -\,0.075\,\rm{dex}/r_e$ with a scatter of $\sigma = 0.016\,\rm{dex}/r_e$ when normalising the distances to the disc effective radius. By performing a set of Kolmogorov-Smirnov tests, we determined that this slope is independent of other galaxy properties, such as morphology, absolute magnitude, and the presence or absence of bars. In particular, barred galaxies do not seem to display shallower gradients, as predicted by numerical simulations. Interestingly, we find that most of the galaxies in the sample with reliable oxygen abundance values beyond $\sim 2$ effective radii (57 galaxies) present a flattening of the abundance gradient in these outer regions. This flattening is not associated with any morphological feature, which suggests that it is a common property of disc galaxies. Finally, we detect a drop or truncation of the abundance in the inner regions of 27 galaxies in the sample; this is only visible for the most massive galaxies.
We study the chemodynamical properties of the Carina dwarf spheroidal by combining an intermediate spectroscopic resolution dataset of more than 900 red giant and red clump stars, with high-precision photometry to derive the atmospheric parameters, metallicities and age estimates for our targets. Within the red giant branch population, we find evidence for the presence of three distinct stellar sub-populations with different metallicities, spatial distributions, kinematics and ages. As in the Fornax and Sculptor dwarf spheroidals, the subpopulation with the lowest average metallicity is more extended and kinematically hotter than all other populations. However, we identify an inversion in the parallel ordering of metallicity, kinematics and characteristic length scale in the two most metal rich subpopulations, which therefore do not contribute to a global negative chemical gradient. Contrary to common trends in the chemical properties with radius, the metal richest population is more extended and mildly kinematically hotter than the main component of intermediate metallicity. More investigations are required to ascertain the nature of this inversion, but we comment on the mechanisms that might have caused it.
Mass models of galactic disks traditionnally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, like e.g. lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk mid-plane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M99, the new strategy shows that circular velocities are highly non-uniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M99, in the usual case where luminous and dark matter share the same centre. The impact of the velocity non-uniformity is to make the inner profile less steep, though the density remains cuspy. On another hand, a model where the halo is core-dominated and shifted by 2.2-2.5 kpc from the luminous mass centre is more appropriate to account for most of the kinematical lopsidedness evidenced in the velocity field of M99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions, maybe a lopsided distribution of dark matter.
Extremely metal-poor (XMP) galaxies are defined to have gas-phase metallicity smaller than a tenth of the solar value (12 + log[O/H] < 7.69). They are uncommon, chemically and possibly dynamically primitive, with physical conditions characteristic of earlier phases of the Universe. We search for new XMPs in the Sloan Digital Sky Survey (SDSS) in a work that complements Paper I. This time high electron temperature objects are selected; since metals are a main coolant of the gas, metal- poor objects contain high-temperature gas. Using the algorithm k-means, we classify 788677 spectra to select 1281 galaxies having particularly intense [OIII]4363 with respect to [OIII]5007, which is a proxy for high electron temperature. The metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 XMPs. A less restrictive noise constraint provides a larger set with 332 candidates. Both lists are provided in electronic format. The selected XMP sample have mean stellar mass around 10^8Msun, with dust-mass \sim 10^3Msun for typical star-forming regions. In agreement with previous findings, XMPs show a tendency to be tadpole-like or cometary. Their underlying stellar continuum corresponds to a fairly young stellar population (< 1Gyr), although young and aged stellar populations co-exists at the low-metallicity starbursts. About 10% of the XMPs shows large N/O. Based on their location in constrained cosmological numerical simulations, XMPs have a strong tendency to appear in voids and to avoid galaxy clusters. The puzzling 2%-solar low-metallicity threshold exhibited by XMPs remains.
Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2 +/- 0.1)% for the RGB, (1.6 +/- 1.1)% for the AGB, and (0.3 +/- 0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval.
We present here a nearly complete census of classical Cepheids in the
Magellanic System. The sample extends the set of Cepheids published in the past
by the Optical Gravitational Lensing Experiment (OGLE) to the outer regions of
the Large (LMC) and Small Magellanic Cloud (SMC). The entire collection
consists of 9535 Cepheids of which 4620 belong to the LMC and 4915 are members
of the SMC. We provide the I- and V-band time-series photometry of the
published Cepheids, their finding charts, and basic observational parameters.
Based on this unique OGLE sample of Cepheids we present the updated
period-luminosity relations for fundamental, first, and second mode of
pulsations in the I and V bands and for the W_I extinction-free Wesenheit
index. We also show the distribution of classical Cepheids in the Magellanic
System. The OGLE collection contains several classical Cepheids in the
Magellanic Bridge - the region of interaction between the Magellanic Clouds.
The discovery of classical Cepheids and their estimated age confirm the
presence of young stellar population between these galaxies.
Accurate and precise measurements of the Hubble constant are critical for testing our current standard cosmological model and revealing possibly new physics. With Hubble Space Telescope (HST) imaging, each strong gravitational lens system with measured time delays can allow one to determine the Hubble constant with an uncertainty of $\sim 7\%$. Since HST will not last forever, we explore adaptive-optics (AO) imaging as an alternative that can provide higher angular resolution than HST imaging but has a less stable point spread function (PSF) due to atmospheric distortion. To make AO imaging useful for time-delay-lens cosmography, we develop a method to extract the unknown PSF directly from the imaging of strongly lensed quasars. In a blind test with two mock data sets created with different PSFs, we are able to recover the important cosmological parameters (time-delay distance, external shear, lens mass profile slope, and total Einstein radius). Our analysis of the Keck AO image of the strong lens system RXJ1131-1231 shows that the important parameters for cosmography agree with those based on HST imaging and modeling within 1-$\sigma$ uncertainties. Most importantly, the constraint on the model time-delay distance by using AO imaging with $0.045"$resolution is tighter by $\sim 50\%$ than the constraint of time-delay distance by using HST imaging with $0.09"$when a power-law mass distribution for the lens system is adopted. Our PSF reconstruction technique is generic and applicable to data sets that have multiple nearby point sources, enabling scientific studies that require high-precision models of the PSF.
We analyse ALMA observations of the 12CO(3-2) emission of the circumstellar envelope (CSE) of the Mira variable binary star W Aql. These provide, for the first time, spatially resolved Doppler velocity spectra of the CSE up to angular distances to the central star of ~ 5" (meaning some 2000 AU). The exploratory nature of the observations (only five minutes in each of two different configurations) does not allow for a detailed modelling of the properties of the CSE but provides important qualitative information on its morphology and kinematics. Emission is found to be enhanced along an axis moving from east/west to north-east/south-west when the angular distance from the central star projected on the plane of the sky increases from zero to four arcseconds. In parallel, the Doppler velocity distribution displays asymmetry along an axis moving from east/west to north-west/south-east. The results are discussed in the context of earlier observations, in particular of the dust morphology.
In order to investigate the Galactic-scale environmental effects on the evolution of protoplanetary disks, we explored the near-infrared (NIR) disk fraction of the Quartet cluster, which is a young cluster in the innermost Galactic disk at the Galactocentric radius Rg ~ 4 kpc. Because this cluster has a typical cluster mass of ~10^3 M_sun as opposed to very massive clusters, which have been observed in previous studies (>10^4 M_sun), we can avoid intra-cluster effects such as strong UV field from OB stars. Although the age of the Quartet is previously estimated to be 3-8 Myr old, we find that it is most likely ~3-4.5 Myr old. In moderately deep JHK images from the UKIDSS survey, we found eight HAeBe candidates in the cluster, and performed K-band medium-resolution ($R \equiv \Delta \lambda / \lambda ~ 800$) spectroscopy for three of them with the Subaru 8.2 m telescope. These are found to have both Br\gamma absorption lines as well as CO bandhead emission, suggesting that they are HAeBe stars with protoplanetary disks. We estimated the intermediate-mass disk fraction (IMDF) to be ~25 % for the cluster, suggesting slightly higher IMDF compared to those for young clusters in the solar neighborhood with similar cluster age, although such conclusion should await future spectroscopic study of all candidates of cluster members.
To explain the accelerated expansion of our universe, many dark energy models and modified gravity theories have been proposed so far. It is argued in the literature that they are difficult to be distinguished on the cosmological scales. Therefore, it is well motivated to consider the relevant astrophysical phenomena on (or below) the galactic scales. In this work, we study the stability of self-gravitating differentially rotating galactic disks in $f(T)$ theory, and obtain the local stability criterions in $f(T)$ theory, which are quite different from the ones in Newtonian gravity, general relativity, and other modified gravity theories such as $f(R)$ theory. We consider that this might be a possible hint to distinguish $f(T)$ theory from general relativity and other modified gravity theories on (or below) the galactic scales.
Links to: arXiv, form interface, find, astro-ph, recent, 1601, contact, help (Access key information)