We study the distribution and evolution of the stellar mass and the star formation rate (SFR) of the brightest group galaxies (BGGs) over $ 0.04<z<1.3 $ using a large sample of $ 407 $ X-ray galaxy groups selected from the COSMOS, AEGIS, and XMM-LSS fields. We compare our results with predictions from the semi-analytic models based on the Millennium simulation. In contrast to model predictions, we find that, as the universe evolves, the stellar mass distribution evolves towards a normal distribution. This distribution tends to skew to low mass BGGs at all redshifts implying the presence of a star-forming population of the BGGs with $ M_S\sim10^{10.5} M_{\odot} $ which results in the shape of the stellar mass distribution deviating from a normal distribution. In agreement with models and previous studies, we find that the mean stellar mass of BGGs grows with time by a factor of $\sim2$ between $z=1.3$ to $z=0.1$, however, the significant growth occurs above $ z=0.4$. The BGGs are not entirely a dormant population of galaxies, as low mass BGGs in low mass halos are more active in forming stars than the BGGs in more massive halos, over the same redshift range. We find that the average SFR of the BGGs evolves steeply with redshift and fraction of the passive BGGs increases as a function of increasing stellar mass and halo mass. Finally, we show that the specific SFR of the BGGs within halos with $ M_{200} \leq 10^{13.4} M_{\odot} $ decreases with increasing halo mass at $ z<0.4 $.
We report 1.1 mm number counts revealed with the Atacama Large Millimeter/submillimeter Array (ALMA) in the Subaru/XMM-Newton Deep Survey Field (SXDF). The advent of ALMA enables us to reveal millimeter-wavelength number counts down to the faint end without source confusion. However, previous studies are based on the ensemble of serendipitously-detected sources in fields originally targeting different sources and could be biased due to the clustering of sources around the targets. We derive number counts in the flux range of 0.2-2 mJy by using 23 (>=4sigma) sources detected in a continuous 2.0 arcmin$^2$ area of the SXDF. The number counts are consistent with previous results within errors, suggesting that the counts derived from serendipitously-detected sources are not significantly biased, although there could be field-to-field variation due to the small survey area. By using the best-fit function of the number counts, we find that ~40% of the extragalactic background light at 1.1 mm is resolved at S(1.1mm) > 0.2 mJy.
Dust polarization in millimeter (and centimeter) has been mapped in disks around an increasing number of young stellar objects. It is usually thought to come from emission by magnetically aligned (non-spherical) grains, but can also be produced by dust scattering. We present a semi-analytic theory of disk polarization that includes both the direction emission and scattering, with an emphasis on their relative importance and how they are affected by the disk inclination. For face-on disks, both emission and scattering tend to produce polarization in the radial direction, making them difficult to distinguish, although the scattering-induced polarization can switch to the azimuthal direction if the incident radiation is beamed strongly enough in the radial direction in the disk plane. Disk inclination affects the polarizations from emission and scattering differently, especially on the major axis where, in the edge-on limit, the former vanishes while the latter reaches a polarization fraction as large as 1/3. The polarizations from the two competing mechanisms tend to cancel each other on the major axis, producing two low polarization "holes" (one on each side of the center) under certain conditions. We find tantalizing evidence for at least one such "hole" in NGC1333 IRAS4A1, whose polarization observed at 8 mm on the 100 AU scale is indicative of a pattern dominated by scattering close to the center and by direction emission in the outer region. If true, it would imply not only that a magnetic field exists on the disk scale, but that it is strong enough to align large, possibly mm-sized, grains.
The lack of arm tracers, especially the remote tracers, is one of the most difficult problems that prevent us studying the Milky Way structure. Fortunately, with its high sensitivity CO survey, the Milky Way Imaging Scroll Painting (MWISP) project offers such an opportunity. As the project has completed about one third of its plan, the area of l=[100,150] deg, b=[-3,5] deg has been nearly covered. And the Outer arm of the Milky Way first clearly revealed its shape in the second galactic quadrant with the form of molecular gas --- this is the first time that the Outer arm is reported in such the large scale mapping of molecular gas. Using the 115 GHz 12CO(1-0) data of MWISP in the LSR velocity ~= [-100,-60] km s^-1 and in the area mentioned above, we have detected 481 molecular clouds in total, among them 332 (about 69\%) are newly detected, and 457 probably belong to the Outer arm. The total mass of the detected Outer arm clouds is ~ 3.1*10^6 M_sun. Assuming the spiral arm is logarithmic spiral, the pitch angle is fitted as ~ 13.1 deg. Besides, combining both the CO data from MWISP and the 21-cm HI data from CGPS, the gas distribution, warp and thickness of the Outer arm are also studied.
Hard X-ray spectra of 28 bright Seyfert galaxies observed with INTEGRAL were analyzed together with the X-ray spectra from XMM-Newton, Suzaku and RXTE. These broad-band data were fitted with a model assuming a thermal Comptonization as a primary continuum component. We tested several model options through a fitting of the Comptonized continuum accompanied by a complex absorption and a Compton reflection. Both the large data set used and the model space explored allowed us to accurately determine a mean temperature kTe of the electron plasma, the Compton parameter y and the Compton reflection strength R for the majority of objects in the sample. Our main finding is that a vast majority of the sample (20 objects) is characterized by kTe < 100 keV, and only for two objects we found kTe > 200 keV. The median kTe for entire sample is 48(-14,+57) keV. The distribution of the y parameter is bimodal, with a broad component centered at ~0.8 and a narrow peak at ~1.1. A complex, dual absorber model improved the fit for all data sets, compared to a simple absorption model, reducing the fitted strength of Compton reflection by a factor of about 2. Modest reflection (median R ~0.32) together with a high ratio of Comptonized to seed photon fluxes point towards a geometry with a compact hard X-ray emitting region well separated from the accretion disc. Our results imply that the template Seyferts spectra used in AGN population synthesis models should be revised.
In this work, we investigate the contribution of dust scattering to the diffuse H-alpha emission observed in nearby galaxies. As initial conditions for the spatial distribution of HII regions, gas, and dust, we take three Milky Way-like galaxies from state-of-the-art cosmological hydrodynamical simulations that implement different prescriptions for star formation, feedback, and chemical enrichment. Radiative transfer has been solved a posteriori, using the publicly-available Monte Carlo code Sunrise to take into account dust absorption and scattering of the H-alpha photons, originating exclusively from the HII regions. No contribution from recombinations in the diffuse ionized gas (DIG) component is explicitly or implicitly included in our model. Our main result is that the flux arising from scattered light is of the order of 1-2 per cent of the H-alpha flux coming directly from the HII regions. Building upon previous studies, we conclude that the DIG contributes lass than 50 per cent of the total H-alpha emission.
Calcium-rich supernovae represent a significant challenge for our understanding of the fates of stellar systems. They are less luminous than other supernova (SN) types and they evolve more rapidly to reveal nebular spectra dominated by strong calcium lines with weak or absent signatures of other intermediate- and iron-group elements, which are seen in other SNe. Strikingly, their explosion sites also mark them out as distinct from other SN types. Their galactocentric offset distribution is strongly skewed to very large offsets (around one third are offset greater than 20 kpc), meaning they do not trace the stellar light of their hosts. Many of the suggestions to explain this extreme offset distribution have invoked the necessity for unusual formation sites such as globular clusters or dwarf satellite galaxies, which are therefore difficult to detect. Building on previous work attempting to detect host systems of nearby Ca-rich SNe, we here present Hubble Space Telescope imaging of 5 members of the class - 3 exhibiting large offsets and 2 coincident with the disk of their hosts. We find no underlying sources at the explosion sites of any of our sample. Combining with previous work, the lack of a host system now appears to be a ubiquitous feature amongst Ca-rich SNe. In this case the offset distribution is most readily explained as a signature of high-velocity progenitor systems that have travelled significant distances before exploding.
We report about recent updates of broad-band properties of radio-loud narrow-line Seyfert 1 galaxies.
The brightest cluster galaxy (BCG) in the majority of relaxed, cool core galaxy clusters is radio loud, showing non-thermal radio jets and lobes ejected by the central active galactic nucleus (AGN). Such relativistic plasma has been unambiguously shown to interact with the surrounding thermal intra-cluster medium (ICM) thanks to spectacular images where the lobe radio emission is observed to fill the cavities in the X-ray-emitting gas. This `radio-mode AGN feedback' phenomenon, which is thought to quench cooling flows, is widespread and is critical to understand the physics of the inner regions of galaxy clusters and the properties of the central BCG. At the same time, mechanically-powerful AGN are likely to drive turbulence in the central ICM which may contribute to gas heating and also play a role for the origin of non-thermal emission on cluster-scales. Diffuse non-thermal emission has been observed in a number of cool core clusters in the form of a radio mini-halo surrounding the radio-loud BCG on scales comparable to that of the cooling region. This contribution outlines the main points covered by the talk on these topics. In particular, after summarizing the cooling flow regulation by AGN heating and the non-thermal emission from cool core clusters, we present a recent study of the largest collection of known mini-halo clusters (~ 20 objects) which investigated the scenario of a common origin of radio mini-halos and gas heating. We further discuss the prospects offered by future radio surveys with the Square Kilometre Array (SKA) for building large (>> 100 objects), unbiased mini-halo samples while probing at the same time the presence of radio-AGN feedback in the host clusters.
PKS 1424+240 is a BL-Lac blazar with unknown redshift that was detected at high-energy gamma rays by Fermi-LAT with a hard spectrum. At VHE, it was first detected by VERITAS and later confirmed by MAGIC. Its spectral energy distribution is highly attenuated at VHE gamma rays, which is coherent with distant sources. Several estimations enabled the redshift to be constrained to the range 0.6 < z < 1.3. These results place PKS 1424+240 in the very interesting condition of being probably the most distant blazar that has been detected at VHE. The ambiguity in the redshift is still large enough to prevent precise studies of the EBL and the intrinsic blazar spectrum. Given the difficulty of measuring spectroscopic redshifts for BL-Lac objects directly, we aim to establish a reliable redshift value for this blazar by finding its host group of galaxies. Elliptical galaxies are associated with groups, and BL-Lac objects are typically hosted by them, so we decided to search for the host group of the blazar. For this, we performed optical spectroscopic observations of thirty objects in the field of view of PKS 1424+240 using the Gemini MOS. After analysing the data for groups, we evaluated the probability of finding groups of galaxies by chance around the position of PKS 1424+240, using a deep catalogue of groups. We also used photometric data from the SDSS catalogue to analyse the red sequence of the proposed blazar host group. We found a new group of galaxies with eight members at z = 0.6010 +- 0.003, a virial radius of R_vir = 1.53 Mpc, and a velocity dispersion of sigma_v = 813 +- 187 km/s. The photometric study indicates that more members are probably populating this previously uncatalogued group of galaxies. The probability of PKS 1424+240 being a member of this group was found to be 98%. The new group of galaxies found at z = 0.6010 +- 0.003 is very likely hosting PKS 1424+240.
The AMBRE Project is a collaboration between the European Southern
Observatory (ESO) and the Observatoire de la Cote d'Azur (OCA) that has been
established in order to carry out the determination of stellar atmospheric
parameters for the archived spectra of four ESO spectrographs.
The analysis of the UVES archived spectra for their stellar parameters has
been completed in the third phase of the AMBRE Project. From the complete
ESO:UVES archive dataset that was received covering the period 2000 to 2010,
51921 spectra for the six standard setups were analysed. The AMBRE analysis
pipeline uses the stellar parameterisation algorithm MATISSE to obtain the
stellar atmospheric parameters. The synthetic grid is currently constrained to
FGKM stars only.
Stellar atmospheric parameters are reported for 12,403 of the 51,921 UVES
archived spectra analysed in AMBRE:UVES. This equates to ~23.9% of the sample
and ~3,708 stars. Effective temperature, surface gravity, metallicity and alpha
element to iron ratio abundances are provided for 10,212 spectra (~19.7%),
while at least effective temperature is provided for the remaining 2,191
spectra. Radial velocities are reported for 36,881 (~71.0%) of the analysed
archive spectra. Typical external errors of sigmaTeff~110dex,
sigmalogg~0.18dex, sigma[M/H]~0.13dex, and sigma[alpha/Fe]~0.05dex with some
reported variation between giants and dwarfs and between setups are reported.
UVES is used to observe an extensive collection of stellar and non-stellar
objects all of which have been included in the archived dataset provided to OCA
by ESO. The AMBRE analysis extracts those objects which lie within the FGKM
parameter space of the AMBRE slow rotating synthetic spectra grid. Thus by
homogeneous blind analysis AMBRE has successfully extracted and parameterised
the targeted FGK stars (23.9% of the analysed sample) from within the ESO:UVES
archive.
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We investigate the mass content of galaxies in the core of the galaxy cluster Abell 611. We perform a strong lensing analysis of the cluster core and use velocity dispersion measurements for individual cluster members as additional constraints. Despite the small number of multiply-imaged systems and cluster members with central velocity dispersions available in the core of A611, the addition of velocity dispersion measurements leads to tighter constraints on the mass associated with the galaxy component, and as a result, on the mass associated with the dark matter halo. Without the spectroscopic velocity dispersions, we would overestimate the mass of the galaxy component by a factor of $\sim1.5$, or, equivalently, we would underestimate the mass of the cluster dark halo by $\sim5\%$. We perform an additional lensing analysis using surface brightness (SB) reconstruction of the tangential giant arc. This approach improves the constraints on the mass parameters of the 5 galaxies close to the arc by up to a factor $\sim10$. The galaxy velocity dispersions resulting from the SB analysis are consistent at the 1$\sigma$ confidence level with the spectroscopic measurements and with the prediction from the simple pointlike analysis. In contrast the truncation radii for 2-3 galaxies depart significantly from the galaxy scaling relation and suggest differences in the stripping history from galaxy to galaxy.
We present an analysis of the morphological classification of 89 luminous infrared galaxies (LIRGs) from the Great Observatories All-sky LIRG Survey (GOALS) sample using non-parametric coefficients and compare their morphology as a function of wavelength. We rely on images obtained in the optical (B- and I-band) as well as in the infrared (H-band and 5.8$\mu$m). Our classification is based on the calculation of $Gini$ and the second order of light ($M_{20}$) non-parametric coefficients which we explore as a function of stellar mass ($M_\star$), infrared luminosity ($L_{IR}$) and star formation rate (SFR). We investigate the relation between $M_{20}$, the specific SFR (sSFR) and the dust temperature ($T_{dust}$) in our galaxy sample. We find that $M_{20}$ is a better morphological tracer than $Gini$, as it allows to distinguish systems formed by double systems from isolated and post-merger LIRGs. The multi-wavelength analysis allows us to identify a region in the $Gini$-$M_{20}$ parameter space where ongoing mergers reside, regardless of the band used to calculate the coefficients. In particular when measured in the H-band, this region can be used to identify ongoing mergers, with a minimal contamination from LIRGs in other stages. We also find that while the sSFR is positively correlated with $M_{20}$ when measured in the mid-infrared, i.e. star-bursting galaxies show more compact emission, it is anti-correlated with the B-band based $M_{20}$. We interpret this as the spatial decoupling between obscured and un-obscured star formation, whereby the ultraviolet/optical size of a LIRGs experience an intense dust enshrouded central starburst is larger than in the one in the mid-infrared since the contrast between the nuclear to the extended disk emission is smaller in the mid-infrared. This has important implications for high redshift surveys of dusty sources. [abridged]
We studied the properties of the neutral gas in a sample of 38 local [U]LIRGs, which mainly covers the less explored LIRG luminosity range. This study is based on the analysis of the spatially integrated and spatially resolved spectra of the NaD feature obtained with the VIMOS/VLT-IFS. Analyzing spatially integrated spectra, we find that the contribution of stars to the observed NaD-EWs is generally small (<35%), and therefore this feature is dominated by ISM absorption. After subtracting the stellar contribution, we find that the pure-ISM integrated spectra generally show blueshifted NaD profiles, indicating neutral gas outflow velocities V in the range 65-260 km/s. Excluding galaxies with AGNs, V shows a dependency with the SFR of the type V \propto SFR^0.15 (in rather good agreement with previous results). The spatially resolved analysis was performed for 40 galaxies, 22 of which have neutral gas velocity fields dominated by noncircular motions with signatures of cone-like winds. However, a modest number of targets (11/40) show disk rotation. We found that the wind masses are in the range (0.4-7.5)x10^8 Msun, reaching up to 3% of the dynamical mass of the host. The mass rates are typically only 0.2-0.4 times the SFR indicating that, the mass loss is too small to slow down the SF significantly. In the majority of cases, the velocity of the outflowing gas is not sufficient to escape the host potential well and, therefore, most of the gas rains back into the disk. On average V/v(esc) is higher in less massive galaxies, confirming that the galaxy mass has a primary role in shaping the recycling of gas and metals. The comparison between the wind power and kinetic power of the starburst associated with SNe indicates that the starburst could drive the outflows in nearly all the [U]LIRGs galaxies, as the wind power is generally lower than 20% of the kinetic power supplied by the starburst.
Using archival data from the 2008 Lick AGN Monitoring Project, Zhang & Feng (2016) claimed to find evidence for flux variations in the narrow [O III] emission of the Seyfert 1 galaxy Mrk 142 over a two-month time span. If correct, this would imply a surprisingly compact size for the narrow-line region. We show that the claimed [O III] variations are merely the result of random errors in the overall flux calibration of the spectra. The data do not provide any support for the hypothesis that the [O III] flux was variable during the 2008 monitoring period.
With ALMA making it possible to resolve giant molecular clouds (GMCs) in other galaxies, it is becoming necessary to quantify the observational bias on measured GMC properties. Using a hydrodynamical simulation of a barred spiral galaxy, we compared the physical properties of GMCs formed in position-position-position space (PPP) to the observational position-position-velocity space (PPV). We assessed the effect of disc inclination: face-on (PPV_face) and edge-on (PPV_edge), and resolution: 1.5 pc versus 24 pc, on GMC properties and the further implications of using Larson's scaling relations for mass-radius and velocity dispersion-radius. The low-resolution PPV data are generated by simulating ALMA Cycle 3 observations using the CASA package. Results show that the median properties do not differ strongly between PPP and PPV_face under both resolutions, but PPV_edge clouds deviate from these two. The differences become magnified when switching to the lower, but more realistic resolution. The discrepancy can lead to opposite results for the virial parameter's measure of gravitational binding, and therefore the dynamical state of the clouds. The power-law indices for the two Larson's scaling relations decrease going from PPP, PPV_face to PPV_edge and decrease from high to low resolutions. We conclude that the relations are not entirely driven by the underlying physical origin and therefore have to be used with caution when considering the environmental dependence, dynamical state, and the extragalactic CO-to-H2 conversion factor of GMCs.
We present the stellar mass functions (SMF) and mass densities of galaxies, and their spheroid and disk components in the local (z~0.1) universe over the range 8.9 <= log(M/M_solar) <= 12 from spheroid+disk decompositions and corresponding stellar masses of a sample of over 600,000 galaxies in the SDSS-DR7 spectroscopic sample. The galaxy SMF is well represented by a single Schechter function (M* = 11.116+/-0.011, alpha = -1.145+/-0.008), though with a hint of a steeper faint end slope. The corresponding stellar mass densities are (2.670+/-0.110), (1.687+/-0.063) and (0.910+/-0.029)x10^8 M_solar Mpc^-3 for galaxies, spheroids and disks respectively. We identify a crossover stellar mass of log(M/M_solar) = 10.3+/-0.030 at which the spheroid and disk SMFs are equal. Relative contributions of four distinct spheroid/disk dominated sub-populations to the overall galaxy SMF are also presented. The mean disk-to-spheroid stellar mass ratio shows a five fold disk dominance at the low mass end, decreasing monotonically with a corresponding increase in the spheroidal fraction till the two are equal at a galaxy stellar mass, log(M/M_solar)=10.479+/-0.013, the dominance of spheroids then grows with increasing stellar mass. The relative numbers of composite disk and spheroid dominated galaxies show peaks in their distributions, perhaps indicative of a preferred galaxy mass. Our characterization of the low redshift galaxy population provides stringent constraints for numerical simulations to reproduce.
The determination of the redshift of extragalactic gamma ray sources is of fundamental importance for the interpretation of their emission models and extragalactic population studies, AGN classification schemes, and to study the interaction with the extragalactic background light. Here we focus on the BL Lac S2 0109+22, recently detected at very high energies. We obtained a high signal-to-noise optical spectrum at Gran Telescopio Canarias for the source over the spectral range 4000-10000 Angstrom, to search for spectral features of the host galaxy and/or of the nuclear source and it was compared with previous observations in order to confirm and/or dispute its redshift determination. We find the S2 0109+22 optical spectrum is well represented by a power law continuum without any absorption or emission feature of Equivalent Width >0.1 Angstrom. Based on the new optical spectrum we are able to set a redshift lower limit z>0.35, assuming the source is hosted by a massive elliptical galaxy typical for this class of sources. The redshift z=0.265 proposed in the literature for this object is most probably referred to a r=18.3 galaxy at 15" from S2 0109. This galaxy could belong to a group of faint galaxies located at z~0.26.
We present post-Newtonian $N$-body simulations on mergers of accreting stellar-mass black holes (BHs), where such general relativistic effects as the pericentre shift and gravitational wave emission are taken into consideration. To elucidate the key physics that regulates mergers of BHs, the dynamical friction and the mass accretion by ambient gas are incorporated. We consider a system composed of ten black holes with initial mass of $30~M_\odot$. As a result, we show that mergers of accreting stellar-mass BHs are classified into four types: a gas drag-driven, an interplay-driven, a three body-driven, or an accretion-driven merger. We find that BH mergers proceed before significant mass accretion, even if the accretion rate is $\sim10$ Eddington accretion rate, and then all BHs can merge into one heavy BH. More specifically, using the simulation results for a wide range of parameters, we derive a critical accretion rate ($\dot{m}_{\rm c}$), below which the BH growth is promoted faster by mergers: $\dot{m}_{\rm c}/\dot{m}_{\rm HL} = 6\times 10^{-3}$ for low-density ambient gas of $n_{\rm gas} \lesssim 10^8 {\rm cm}^{-3}$, and $\dot{m}_{\rm c}/\dot{m}_{\rm HL} = 2\times 10^{-3} (n_\mathrm{gas}/10^{8} \mathrm{cm}^{-3})^{-1.0} (\rho_\mathrm{BH}/10^6 M_\odot \mathrm{pc}^{-3})^{0.74}$ for $n_{\rm gas} \gtrsim 10^8 {\rm cm}^{-3}$, where $\dot{m}_{\rm HL}$ is the Hoyle-Lyttleton mass accretion rate. Very recently, a gravitational wave event, GW150914, as a result of the merger of a $\sim 30~M_\odot$ BH binary has been detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) (Abbott et al. 2016). Based on the present simulations, the BH merger in GW150914 is likely to be driven by three-body encounters accompanied by a few $M_\odot$ of gas accretion.
Using samples of AGNs, normal galaxies and groups of galaxies selected from the Sloan Digital Sky Survey (SDSS), we study the environments of type 1 and type 2 AGNs both on small and large scales. Comparisons are made for samples matched in redshift, r-band luminosity, and [OIII] luminosity, and separately for central and satellite galaxies. We find that type 2 AGNs and normal galaxies reside in similar environments. Type 1 and type 2 AGNs have similar clustering properties on large scales, but at scales smaller than 100 kpc, type 2s have 3 times more neighbors than type 1s. These results suggest that type 1 and type 2 AGNs are hosted by halos of similar masses, as is also seen directly from the mass distributions of their host groups. Type 2s have significantly more satellites around them, and the distribution of their satellites is also more centrally concentrated. The host galaxies of both types of AGNs have similar optical properties, but their infrared colors are significantly different. Our results suggest that the simple unified model based solely on torus orientation is not sufficient, but that galaxy interactions in dark matter halos must have played an important role in the formation of the dust structure that obscures AGNs.
In this paper we notice that extragalactic sources seem to have non-zero
proper motions in the PPMXL proper motion catalog. We collect a large, all-sky
sample of extragalactic objects and fit their reported PPMXL proper motions to
an ensemble of spherical harmonics in magnitude shells. A magnitude dependent
proper motion correction is thus constructed.
This correction is applied to a set of fundamental radio sources, quasars,
and is compared to similar corrections to assess its utility. We publish, along
with this paper, code which may be used to correct proper motions in the PPMXL
catalog over the full sky which have 2 Micron All Sky Survey photometry.
Pure disk galaxies without any bulge component, i.e., neither classical nor
pseudo, seem to have escaped the affects of merger activity inherent to
hierarchical galaxy formation models as well as strong internal secular
evolution.
We discover that a significant fraction (15 - 18 %) of disk galaxies in the
Hubble Deep Field (0.4 < z < 1.0) as well as in the local Universe (0.02 < z <
0.05) are such pure disk systems (hereafter, PDS). The spatial distribution of
light in these PDS is well described by a single exponential function from the
outskirts to the centre and appears to have remained intact over the last 8
billion years keeping the mean central surface brightness and scale-length
nearly constant. These two disk parameters of PDS are brighter and shorter,
respectively, than of those disks which are part of disk galaxies with bulges.
Since the fraction of PDS as well as their profile defining parameters do not
change, it indicates that these galaxies have not witnessed either major
mergers or multiple minor mergers since z~1. However, there is substantial
increase in their total stellar mass and total size over the same time range.
This suggests that smooth accretion of cold gas via cosmic filaments is the
most probable mode of their evolution. We speculate that PDS are dynamically
hotter and cushioned in massive dark matter halos which may prevent them from
undergoing strong secular evolution.
The reactions of carbon atoms with dihydrogen have been investigated in liquid helium droplets at $T$ = 0.37 K. A calorimetric technique was applied to monitor the energy released in the reaction. The barrierless reaction between a single carbon atom and a single dihydrogen molecule was detected. Reactions between dihydrogen clusters and carbon atoms have been studied by high-resolution mass spectrometry. The formation of hydrocarbon cations of the type C$_m$H$_n^+$, with $m$ = 1-4 and $n$ = 1-15 was observed. With enhanced concentration of dihydrogen, the mass spectra demonstrated the main "magic" peak assigned to the CH$_5^+$ cation. A simple formation pathway and the high stability of this cation suggest its high abundance in the interstellar medium.
We present $^{12}$CO(1-0) and $^{12}$CO(2-1) observations of a sample of 20 star-forming dwarfs selected from the Herschel Virgo Cluster Survey, with oxygen abundances ranging from 12 + log(O/H) ~ 8.1 to 8.8. CO emission is observed in ten galaxies and marginally detected in another one. CO fluxes correlate with the FIR 250 $\mu$m emission, and the dwarfs follow the same linear relation that holds for more massive spiral galaxies extended to a wider dynamical range. We compare different methods to estimate H2 molecular masses, namely a metallicity-dependent CO-to-H2 conversion factor and one dependent on H-band luminosity. The molecular-to-stellar mass ratio remains nearly constant at stellar masses <~ 10$^9$ M$_{\odot}$, contrary to the atomic hydrogen fraction, M$_{HI}$/M$_*$, which increases inversely with M$_*$. The flattening of the M$_{H_2}$/M$_*$ ratio at low stellar masses does not seem to be related to the effects of the cluster environment because it occurs for both HI-deficient and HI-normal dwarfs. The molecular-to-atomic ratio is more tightly correlated with stellar surface density than metallicity, confirming that the interstellar gas pressure plays a key role in determining the balance between the two gaseous components of the interstellar medium. Virgo dwarfs follow the same linear trend between molecular gas mass and star formation rate as more massive spirals, but gas depletion timescales, $\tau_{dep}$, are not constant and range between 100 Myr and 6 Gyr. The interaction with the Virgo cluster environment is removing the atomic gas and dust components of the dwarfs, but the molecular gas appears to be less affected at the current stage of evolution within the cluster. However, the correlation between HI deficiency and the molecular gas depletion time suggests that the lack of gas replenishment from the outer regions of the disc is lowering the star formation activity.
We use a sample of 97 galaxies selected from the ALFALFA 21cm survey to make an accurate measurement of the baryonic Tully-Fisher relation (BTFR). These galaxies are specifically selected to be heavily gas-dominated (Mgas/M* >~ 2.7) and to be oriented edge-on. The former property ensures that the error on the galactic baryonic mass is small, despite the large systematic uncertainty involved in galactic stellar mass estimates. The latter property means that rotational velocities can be derived directly from the width of the 21cm emission line, without any need for inclination corrections. The resulting linewidth-based BTFR has a slope of alpha = 3.58 +- 0.11, a value that is in agreement with previous literature results. The relation is remarkably tight, with almost all galaxies being located within a perpendicular distance of +- 0.1 dex from the best fit line. The low observational error budget for our sample allows us to establish that, despite its tightness, the measured linewidth-based BTFR has some small (i.e., non-zero) intrinsic scatter. We furthermore find a systematic difference in the BTFR of galaxies with "double-horned" 21cm line profiles --suggestive of flat outer galactic rotation curves-- and those with "peaked" profiles --suggestive of rising rotation curves. Restricting our sample to galaxies in the former category results in a slightly steeper slope of alpha = 3.94 +- 0.14. Overall, the high-accuracy measurement of the BTFR presented in this article is intended as a reliable observational benchmark against which to test theoretical expectations. Here we consider a representative set of semi-analytic models and hydrodynamic simulations in the LCDM context, as well as MOND. In the near future, interferometric follow-up observations of several sample members will allow us to further refine the BTFR measurement, and make sharper comparisons with theoretical models.
We discuss our current understanding of the nature of the faint, high-frequency radio sky. The Tenth Cambridge (10C) survey at 15.7 GHz is the deepest high-frequency radio survey to date, covering 12 square degrees to a completeness limit of 0.5 mJy, making it the ideal starting point from which to study this population. In this work we have matched the 10C survey to several lower-frequency radio catalogues and a wide range of multi-wavelength data (near- and far-infrared, optical and X-ray). We find a significant increase in the proportion of flat-spectrum sources at flux densities below 1 mJy - the median radio spectral index between 15.7 GHz and 610 MHz changes from 0.75 for flux densities greater than 1.5 mJy to 0.08 for flux densities less than 0.8 mJy. The multi-wavelength analysis shows that the vast majority (> 94 percent) of the 10C sources are radio galaxies; it is therefore likely that these faint, flat spectrum sources are a result of the cores of radio galaxies becoming dominant at high frequencies. We have used new observations to extend this study to even fainter flux densities, calculating the 15.7-GHz radio source count down to 0.1 mJy, a factor of five deeper than previous studies. There is no evidence for a new population of sources, showing that the high-frequency sky continues to be dominated by radio galaxies down to at least 0.1 mJy.
Aims: We aim to find torus models that explain the observed high-resolution
mid-infrared (MIR) measurements of active galactic nuclei (AGN). Our goal is to
determine the general properties of the circumnuclear dusty environments.
Methods: We used the MIR interferometric data of a sample of AGNs provided by
the instrument MIDI/VLTI and followed a statistical approach to compare the
observed distribution of the interferometric data with the distributions
computed from clumpy torus models. We mainly tested whether the diversity of
Seyfert galaxies can be described using the Standard Model idea. In addition to
line-of-sight (LOS) effects, we performed different realizations of the same
model to include possible variations that are caused by the stochastic nature
of the dusty models.
Results: We find that our entire sample of AGNs, which contains both Seyfert
types, cannot be explained merely by an inclination effect and by including
random variations of the clouds. Instead, we find that each subset of Seyfert
type can be explained by different models, where the filling factor at the
inner radius seems to be the largest difference. For type I objects we find
that about two thirds of our objects could also be described using a dusty
torus similar to the type II objects. For the remaining third, it was not
possible to find a good description using models with high filling factors,
while we found good fits with models with low filling factors.
Conclusions: Within our model assumptions, we did not find one single set of
model parameters that could simultaneously explain the MIR data of all 21 AGN
with LOS effects and random variations alone. We conclude that at least two
distinct cloud configurations are required to model the differences in Seyfert
galaxies, with volume-filling factors differing by a factor of about 5-10. A
continuous transition between the two types cannot be excluded.
We analyzed a sample of 9418 fundamental-mode and first-overtone classical
Cepheids from the OGLE-IV Collection of Classical Cepheids. The distance to
each Cepheid was calculated using the period-luminosity relation for the
Wesenheit magnitude, fitted to our data. The classical Cepheids in the LMC are
situated mainly in the bar and in the northern arm. The eastern part of the LMC
is closer to us and the plane fit to the whole LMC sample yields the
inclination i=24.2+-0.6 deg and position angle P.A.=151.4+-1.5 deg.
We redefined the LMC bar by extending it in the western direction and found
no offset from the plane of the LMC contrary to previous studies. On the other
hand, we found that the northern arm is offset from a plane by about -0.5 kpc,
which was not observed before. The age distribution of the LMC Cepheids shows
one maximum at about 100 Myr.
We demonstrate that the SMC has a non-planar structure and can be described
as an extended ellipsoid. We identified two large ellipsoidal off-axis
structures in the SMC. The northern one is located closer to us and is younger,
while the south-western is farther and older. The age distribution of the SMC
Cepheids is bimodal with one maximum at 110 Myr, and another one at 220 Myr.
Younger stars are located in the closer part of this galaxy while older ones
are more distant.
We classified nine Cepheids from our sample as Magellanic Bridge objects.
These Cepheids show a large spread in three-dimensions although five of them
form a connection between the Clouds. The closest one is closer than any of the
LMC Cepheids, while the furthest one -- farther than any SMC Cepheid. All but
one Cepheids in the Magellanic Bridge are younger than 300 Myr. The oldest one
can be associated with the SMC Wing.
The angular correlation function is a powerful tool for deriving the clustering properties of AGN and hence the mass of the corresponding dark matter halos in which they reside. However, studies based on the application of the angular correlation function on X-ray samples, yield results apparently inconsistent with those based on the direct estimation of the spatial correlation function. The goal of the present paper is to attempt to investigate this issue by analysing a well defined sample. To this end we use the hard-band (2-10 keV) X-ray selected sources of the Chandra AEGIS fields, chosen because of the availability of accurately derived flux sensitivity maps. In particular we use the 186 hard-band sources with spectroscopic redshifts in the range z=0.3-1.3, a range selected in order to contain the bulk of the AGN while minimizing the contribution of unknown clustering and luminosity evolution from very high redshifts. Using the projected spatial auto-correlation function, we derive a clustering comoving length of 5.4+-1.0 Mpc (for gamma=1.8), consistent with results in the literature. We further derive the angular correlation function and the corresponding spatial clustering length using the Limber's inversion equation and a novel parametrization of the clustering evolution model that also takes into account the bias evolution of the host dark matter halo. The Limber's inverted spatial comoving clustering length of 5.5+-1.2 Mpc at a median redshift of z~0.75, matches the directly measured one, from the spatial correlation function analysis, but for a significant non-linear contribution to the growing mode of perturbations, estimated independently from literature results of x_0 at different redshifts. Therefore, using this sample of X-ray AGN and our clustering evolution parametrization we have found an excellent consistency between the angular and spatial clustering analysis.
B and L violating interactions of ordinary particles with their twin particles from hypothetical mirror world can co-generate baryon asymmetries in both worlds in comparable amounts, $\Omega'_B/\Omega_B \sim 5$ or so. On the other hand, the same interactions induce the oscillation phenomena between the neutral particles of two sectors which convert e.g. mirror neutrons into our antineutrons. These oscillations are environment dependent and can have fascinating physical consequences.
We propose the use of the kinetic Sunyaev-Zel'dovich (kSZ) effect to probe the circumgalactic medium (CGM), with the aid of a spectroscopic survey covering the same area of a SZ survey. One can design an optimal estimator of the kSZ effect of the CGM with a matched filter, and construct the cross correlation between the estimator and the peculiar velocity recovered from the galaxy survey, which can be measured by stacking a number of galaxies. We investigate two compelling profiles for the CGM, the MB profile (Maller & Bullock 2004) and the $\beta$ profile, and estimate the detectability against the synergy of a fiducial galaxy survey with number density $10^{-3}h^3\,$ Mpc$^{-3}$ and an ACT-like SZ survey. We show that the shape of the filter does not change much with redshift for the $\beta$ profile, while there are significant side lobes at $z<0.1$ for the MB profile. By stacking $\sim 10^4$ Milky Way-size halos around z $\sim 0.5$, one can get $\gtrsim$ 1 $\sigma$ signal to noise (S/N) for the both profiles. The S/N increases with decreasing redshift before it reaches a maximum ($\sim$ 7.5 at z $\simeq$ 0.15 for the MB profile, $\sim 19$ at $z\simeq 0.03$ for the $\beta$ profile). Due to the large beam size, a Planck-like CMB survey can marginally detect the kSZ signal by stacking the same number of galaxies at $z<0.1$. The search for the CGM in realistic surveys will involve dividing the galaxies into subsamples with similar redshift and mass of host halos, and scaling the results presented here to obtain the S/N.
The VISTA near infrared Y, J, Ks survey of the Magellanic System (VMC) is collecting deep Ks band time series photometry of pulsating variable stars hosted by the two Magellanic Clouds and their connecting Bridge. In this paper, we present Y, J, Ks light curves for a sample of 4172 Small Magellanic Cloud (SMC) Classical Cepheids (CCs). These data, complemented with literature V values, allowed us to construct a variety of period-luminosity (PL), period-luminosity-color (PLC), and period-wesenheit (PW) relationships, valid for Fundamental (F), First Overtone (FO) and Second Overtone (SO) pulsators. The relations involving V, J, Ks bands are in agreement with their counterparts in the literature. As for the Y band, to our knowledge we present the first CC PL, PW, and PLC relations ever derived using this filter. We also present the first near infrared PL, PW, and PLC relations for SO pulsators to date. We used PW(V,Ks) to estimate the relative SMC-LMC distance and, in turn, the absolute distance to the SMC. For the former quantity we find a value of Delta(mu)=0.55+-0.04 mag, in rather good agreement with other evaluations based on CCs, but significantly larger than the results obtained from older population II distance indicators. This discrepancy might be due to the different geometric distributions of young and old tracers in both Clouds. As for the absolute distance to the SMC, our best estimates are mu(SMC)=19.01+-0.05 mag and mu(SMC)=19.04+-0.06 mag, based on two distance measurements to the LMC, which rely on accurate CC and eclipsing Cepheid binary data, respectively.
In synchrotron radiation there is a paradox whether or not the pitch angle of a radiating charge varies. The conventional wisdom is that the pitch angle does not change during the radiation process. The argument is based on Larmor's radiation formula, where in a synchrotron case the radiation power is along the instantaneous direction of motion of the charge. Then the momentum loss will also be parallel to that direction and therefore the pitch angle of the charge would remain unaffected. The accordingly derived formulas for energy losses of synchrotron electrons in radio galaxies are the standard text-book material for the last 50 years. However, if we use the momentum transformation laws from special relativity, then we find that the pitch angle of a radiating charge varies. While the velocity component parallel to the magnetic field remains unaffected, the perpendicular component does reduce in magnitude due to radiative losses, implying a change in the pitch angle. This apparent paradox is resolved when effects on the charge motion are calculated not from Larmor's formula but from Lorentz's radiation reaction formula. We derive the exact formulation by taking into account the change of the pitch angle due to radiative losses. From this we first time derive the characteristic decay time of synchrotron electrons over which they turn from highly relativistic into mildly relativistic ones.
Pre-recombination acoustic oscillations induce an initial relative velocity $v_{cb}$ between baryons and dark matter. We show that the leading effect on galaxy clustering at lower redshifts is induced by its divergence $\theta_{cb} = \partial_i v_{cb}^i$, and estimate the magnitude of this new effect through a spherical collapse calculation. We then derive all streaming velocity contributions to the galaxy power spectrum at 1-loop order, leading to several new terms. Including all these contributions will be essential to avoid a bias in future efforts to use the baryon acoustic oscillation feature in galaxy clustering as standard ruler.
In this article we revisit the significance of the often debated structural similarity between the equations of electromagnetism and fluid dynamics. Although the matching of the two sets of equations has successfully been done for non-dissipative forms of the equations, little has been done for cases where the dissipative terms are non-negligible. We consider the consequence of non-negligible viscosity and diffusivity, and how the fine-tuning of these parameters could allow fluid dynamics to be used to indirectly study certain properties of magnetic fields.
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X-shaped or peanut-shaped (X/P) bulges are observed in more than 40% of (nearly) edge-on disc galaxies, though to date a robust method to quantify them is lacking. Using Fourier harmonics to describe the deviation of galaxy isophotes from ellipses, we demonstrate with a sample of 11 such galaxies (including NGC 128) that the sixth Fourier component ($B_6$) carries physical meaning by tracing this X/P structure. We introduce five quantitative diagnostics based on the radial $B_6$ profile, namely: its `peak' amplitude ($\Pi_{\rm max}$); the (projected major-axis) `length' where this peak occurs ($R_{\Pi,max}$); its vertical `height' above the disc plane ($z_{\Pi,max}$); the $B_6$ profile's integrated `strength' ($S_{\Pi}$); and the $B_6$ peak `width' ($W_{\Pi}$). We also introduce different `classes' of $B_6$ profile shape. Furthermore, we convincingly detect and measure the properties of multiple (nested) X/P structures in individual galaxies which additionally display the signatures of multiple bars in their surface brightness profiles, thus consolidating further the scenario in which peanuts are associated with bars. We reveal that the peanut parameter space (`length', `strength' and `height') for real galaxies is not randomly populated, but the 3 metrics are inter-correlated (both in kpc and disc scale-length $h$). Additionally, the X/P `length' and `strength' appear to correlate with $v_{rot}/\sigma_*$, lending further support to the notion that peanuts `know' about the galactic disc in which they reside. Such constraints are important for simulations, as they provide a direct link between peanuts and their host disc. Our diagnostics reveal a spectrum of X/P properties and could provide a means of distinguishing between different peanut formation scenarios. Moreover, nested peanuts, as remnants of bar buckling events, can provide insights into the disc and bar instability history.
Massive gas-rich galaxy discs at $z \sim 1-3$ host massive star-forming clumps with typical baryonic masses in the range $10^7-10^8$ M$_{\odot}$ which can affect the orbital decay and concurrent growth of supermassive black hole (BH) pairs. We use a set of high-resolution simulations of isolated clumpy galaxies hosting a pair of unequal-mass BHs, in order to study the interaction between massive clumps and a BH pair at kpc scales, during the early phase of the orbital decay, before the formation of a bound BH binary. We find that both the interaction with massive clumps and the heating of the cold gas layer of the disc by BH feedback tend to delay significantly the orbital decay of the secondary, which in many cases is ejected and then hovers for a whole Gyr around a separation of 1-2 kpc. In the envelope, dynamical friction is weak and there is no contribution of disc torques: these lead to the fastest decay once the orbit of the secondary BH has circularised in the disc midplane. In runs with larger eccentricities the delay is stronger, although there are some exceptions. We also show that, even in discs with very sporadic transient clump formation, a strong spiral pattern appears to be enough in order to affect the decay time-scale for BHs on eccentric orbits. We conclude that, contrary to previous belief, a gas-rich background is not necessarily conducive to a fast BH decay and binary formation, which prompts more extensive investigations aimed at calibrating event-rate forecasts for ongoing and future gravitational-wave searches, such as with Pulsar Timing Arrays (PTAs) and the future evolved Laser Interferometer Space Antenna (eLISA).
The Milky Way bulge has a boxy/peanut morphology and an X-shaped structure. This X-shape has been revealed by the `split in the red clump' from star counts along the line of sight toward the bulge, measured from photometric surveys. This boxy, X-shaped bulge morphology is not unique to the Milky Way and such bulges are observed in other barred spiral galaxies. N-body simulations show that boxy and X-shaped bulges are formed from the disk via dynamical instabilities. It has also been proposed that the Milky Way bulge is not X-shaped, but rather, the apparent split in the red clump stars is a consequence of different stellar populations, in an old classical spheroidal bulge. We present a WISE image of the Milky Way bulge, produced by downsampling the publicly available "unWISE" coadds. The WISE image of the Milky Way bulge shows that the X-shaped nature of the Milky Way bulge is self-evident and irrefutable. The X-shape morphology of the bulge in itself and the fraction of bulge stars that comprise orbits within this structure has important implications for the formation history of the Milky Way, and, given the ubiquity of boxy X-shaped bulges, spiral galaxies in general.
We compare the predictions of a semi-analytic model for ultra-compact dwarf galaxy (UCD) formation by tidal stripping to the observed properties of globular clusters (GCs) and UCDs in the Fornax and Virgo clusters. For Fornax we find the predicted number of stripped nuclei agrees very well with the excess number of GCs$+$UCDs above the GC luminosity function. GCs$+$UCDs with masses $>10^{7.3}$ M$_\odot$ are consistent with being entirely formed by tidal stripping. Stripped nuclei can also account for Virgo UCDs with masses $>10^{7.3}$ M$_\odot$ where numbers are complete by mass. For both Fornax and Virgo, the predicted velocity dispersions and radial distributions of stripped nuclei are consistent with that of UCDs within $\sim$50-100 kpc but disagree at larger distances where dispersions are too high and radial distributions too extended. Stripped nuclei are predicted to have radially biased anisotropies at all radii, agreeing with Virgo UCDs at clustercentric distances larger than 50 kpc. However, ongoing disruption is not included in our model which would cause orbits to become tangentially biased at small radii. We find the predicted metallicities and central black hole masses of stripped nuclei agree well with the metallicities and implied black hole masses of UCDs for masses $>10^{6.5}$ M$_\odot$. The predicted black hole masses also agree well with that of M60-UCD1, the first UCD with a confirmed central black hole. These results suggest that observed GC$+$UCD populations are a combination of genuine GCs and stripped nuclei, with the contribution of stripped nuclei increasing toward the high-mass end.
We introduce a new suite of radiation-hydrodynamical simulations of galaxy formation and reionization called Aurora. The Aurora simulations make use of a spatially adaptive radiative transfer technique that lets us accurately capture the small-scale structure in the gas at the resolution of the hydrodynamics, in cosmological volumes. In addition to ionizing radiation, Aurora includes galactic winds driven by star formation and the enrichment of the universe with metals synthesized in the stars. Our reference simulation uses 2x512^3 dark matter and gas particles in a box of size 25 comoving Mpc/h with a force softening scale of at most 0.28 kpc/h. It is accompanied by simulations in larger and smaller boxes and at higher and lower resolution, employing up to 2x1024^3 particles, to investigate numerical convergence. All simulations are calibrated to yield simulated star formation rate (SFR) functions in close agreement with observational constraints at redshift z = 7 and to achieve reionization at z = 8.3, which is consistent with the observed optical depth to reionization. We focus on the design and calibration of the simulations and present some first results. The median stellar metallicities of low-mass galaxies at z = 6 are consistent with the metallicities of dwarf galaxies in the Local Group, which are believed to have formed most of their stars at high redshifts. After reionization, the mean photoionization rate decreases strongly with increasing resolution. This is mainly due to the increased abundance of small-scale gaseous systems absorbing ionizing radiation.
A sample of 102 local (0.02 < z < 0.1) Seyfert galaxies with black hole masses MBH > 10^7 M_sun was selected from the Sloan Digital Sky Survey (SDSS) and observed using the Keck 10-m telescope to study the scaling relations between MBH and host galaxy properties. We study profile changes of the broad Hbeta emission line within the ~3-9 year time-frame between the two sets of spectra. The variability of the broad Hbeta emission line is of particular interest, not only since it is used to estimate MBH, but also since its strength and width is used to classify Seyfert galaxies into different types. At least some form of broad-line variability (in either width or flux) is observed in the majority (~66%) of the objects, resulting in a Seyfert-type change for ~38% of the objects, likely driven by variable accretion and/or obscuration. The broad Hbeta line virtually disappears in 3/102 (~3%) extreme cases. We discuss potential causes for these changing-look AGNs. While similar dramatic transitions have previously been reported in the literature, either on a case-by-case basis or in larger samples focusing on quasars at higher redshifts, our study provides statistical information on the frequency of H$\beta$ line variability in a sample of low-redshift Seyfert galaxies.
General aspects about the thermodynamics of astrophysical systems are discussed, overall, those concerning to astrophysical systems in mutual interaction (or the called \emph{open astrophysical systems}). A special interest is devoted along the paper to clarify several misconceptions that are still common in the recent literature, such as the direct application to the astrophysical scenario of notions and theoretical frameworks that were originally conceived to deal with extensive systems of the everyday practice (large systems with short-range interactions).
We present a detailed study of the optical spectroscopic properties of 12 active galactic nuclei (AGNs) with candidate low-mass black holes (BHs) selected by Kamizasa et al. through rapid X-ray variability. The high-quality, echellette Magellan spectra reveal broad H$\alpha$ emission in all the sources, allowing us to estimate robust viral BH masses and Eddington ratios for this unique sample. We confirm that the sample contains low-mass BHs accreting at high rates: the median $M_{\rm BH} = 1.2\times 10^6M_\odot$ and median $L_{\rm bol}/L_{\rm Edd}=0.44$. The sample follows the $M_{\rm BH}-\sigma_*$ relation, within the considerable scatter typical of pseudobulges, the probable hosts of these low-mass AGNs. Various lines of evidence suggest that ongoing star formation is prevalent in these systems. We propose a new strategy to estimate star formation rates in AGNs hosted by low-mass, low-metallicity galaxies, based on modification of an existing method using the strength of [O II] $\lambda 3727$, [O III] $\lambda 5007$, and X-rays.
New high-resolution r band imaging of the brightest cluster galaxy (BCG) in Abell 85 (Holm 15A) was obtained using the Gemini Multi Object Spectrograph. These data were taken with the aim of deriving an accurate surface brightness profile of the BCG of Abell 85, in particular its central region. The new Gemini data show clear evidence of a previously unreported nuclear emission that is evident as a distinct light excess in the central kiloparsec of the surface brightness profile. We find that the light profile is never flat nor does it present a downward trend towards the center of the galaxy. That is, the new Gemini data show a different physical reality from the featureless, "evacuated core" recently claimed for the Abell 85 BCG. After trying different models, we find that the surface brightness profile of the BCG of Abell 85 is best fit by a double Sersic model.
We report on the discovery of broad Balmer absorption lines variability in the QSO SDSS J125942.80+121312.6, based on the optical and near-infrared spectra taken from the SDSS-I, SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and TripleSpec observations over a timescale of 5.8 years in the QSO's rest-frame. The blueshifted absorption profile of H$\beta$ shows a variation of more than 5$\sigma$ at a high velocity portion ($>3000\ \mathrm{km\ s}^{-1}$) of the trough. We perform a detailed analysis for the physical conditions of the absorber using Balmer lines as well as metastable He I and optical Fe II absorptions ($\lambda 4233$ from b$^4$P$_{5/2}$ level and $\lambda 5169$ from a$^6$S$_{5/2}$) at the same velocity. These Fe II lines are identified in the QSO spectra for the first time. According to the photoionization simulations, we estimate a gas density of $n(\mathrm{H})\approx 10^{9.1}\ \mathrm{cm}^{-3}$ and a column density of $N_{\mathrm{col}}(\mathrm{H})\approx 10^{23}\ \mathrm{cm}^{-2}$ for the BOSS data, but the model fails to predict the variations of ionic column densities between the SDSS and BOSS observations if changes in ionizing flux are assumed. We thus propose transverse motion of the absorbing gas being the cause of the observed broad Balmer absorption line variability. In fact, we find that the changes in covering factors of the absorber can well-reproduce all of the observed variations. The absorber is estimated $\sim 0.94$ pc away from the central engine, which is where the outflow likely experiences deceleration due to the collision with the surrounding medium. This scheme is consistent with the argument that LoBAL QSOs may represent the transition from obscured star-forming galaxies to classic QSOs.
Using a spectroscopically confirmed sample of M-giants, M-dwarfs and quasars from the LAMOST survey, we assess how well WISE $\&$ 2MASS color-cuts can be used to select M-giant stars. The WISE bands are very efficient at separating M-giants from M-dwarfs and we present a simple classification that can produce a clean and relatively complete sample of M-giants. We derive a new photometric relation to estimate the metallicity for M-giants, calibrated using data from the APOGEE survey. We find a strong correlation between the $(W1-W2)$ color and $\rm [M/H]$, where almost all of the scatter is due to photometric uncertainties. We show that previous photometric distance relations, which are mostly based on stellar models, may be biased and devise a new empirical distance relation, investigating trends with metallicity and star formation history. Given these relations, we investigate the properties of M-giants in the Sagittarius stream. The offset in the orbital plane between the leading and trailing tails is reproduced and, by identifying distant M-giants in the direction of the Galactic anti-center, we confirm that the previously detected debris in the outer halo is the apocenter of the trailing tail. We also find tentative evidence supporting an existing overdensity near the leading tail in the Northern Galactic hemisphere, possibly an extension to the trailing tail (so-called Branch C). We have measured the metallicity distribution along the stream, finding a clear metallicity offset between the leading and trailing tails, in agreement with models for the stream formation. We include an online table of M-giants to facilitate further studies.
According to the current cosmological cold dark matter paradigm, the Galactic halo could have been the result of the assemblage of smaller structures. Here we explore the hypothesis that the classical and ultra-faint dwarf spheroidal satellites of the Milky Way have been the building blocks of the Galactic halo by comparing their [$\alpha$/Fe] and [Ba/Fe] versus [Fe/H] patterns with the ones observed in Galactic halo stars. The $\alpha$ elements deviate substantially from the observed abundances in the Galactic halo stars for [Fe/H] values larger than -2 dex, while they overlap for lower metallicities. On the other hand, for the [Ba/Fe] ratio the discrepancy is extended at all [Fe/H] values, suggesting that the majority of stars in the halo are likely to have been formed in situ. Therefore, we suggest that [Ba/Fe] ratios are a better diagnostic than [$\alpha$/Fe] ratios. Moreover, for the first time we consider the effects of an enriched infall of gas with the same chemical abundances as the matter ejected and/or stripped from dwarf satellites of the Milky Way on the chemical evolution of the Galactic halo. We find that the resulting chemical abundances of the halo stars depend on the assumed infall time scale, and the presence of a threshold in the gas for star formation. In particular, in models with an infall timescale for the halo around 0.8 Gyr coupled with a threshold in the surface gas density for the star formation (4 $\mathrm{M}_{\odot}\,\mathrm{pc}^{-2}$), and the enriched infall from dwarf spheroidal satellites, the first halo stars formed show [Fe/H]$>$-2.4 dex. In this case, to explain [$\alpha$/Fe] data for stars with [Fe/H]$<$-2.4 dex we need stars formed in dSph systems.
The total number of globular clusters (GCs) in a galaxy rises continuously with the galaxy luminosity L, while the relative number of galaxies decreases with L following the Schechter function. The product of these two very nonlinear functions gives the relative number of GCs contained by all galaxies at a given L. It is shown that GCs, in this universal sense, are most commonly found in galaxies within a narrow range around $L_{\star}$. In addition, blue (metal-poor) GCs outnumber the red (metal-richer) ones globally by 4 to 1 when all galaxies are added, pointing to the conclusion that the earliest stages of galaxy formation were especially favorable to forming massive, dense star clusters.
Ionized regions around early-type stars are believed to be well-known objects, but until recently, our knowledge of the relation between the free-free radio emission and the IR emission has been observationally hindered by the limited angular resolution in the far-IR. The advent of Herschel has now made it possible to obtain a more precise comparison between the two regimes, and it has been found that about a third of the young HII regions emit more Lyman continuum photons than expected, thus presenting a Lyman excess. With the present study we wish to distinguish between two scenarios that have been proposed to explain the existence of the Lyman excess: (i) underestimation of the bolometric luminosity, or (ii) additional emission of Lyman-continuum photons from an accretion shock. We observed an outflow (SiO) and an infall (HCO+) tracer toward a complete sample of 200 HII regions, 67 of which present the Lyman excess. Our goal was to search for any systematic difference between sources with Lyman excess and those without. While the outflow tracer does not reveal any significant difference between the two subsamples of HII regions, the infall tracer indicates that the Lyman-excess sources are more associated with infall signposts than the other objects. Our findings indicate that the most plausible explanation for the Lyman excess is that in addition to the Lyman continuum emission from the early-type star, UV photons are emitted from accretion shocks in the stellar neighbourhood. This result suggests that high-mass stars and/or stellar clusters containing young massive stars may continue to accrete for a long time, even after the development of a compact HII region.
We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H]=-1.62+/-0.09) star HD94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s-process; e.g., [Pb/Fe]=+0.79+/-0.32) and rapid neutron-capture process (r-process; e.g., [Eu/Fe]=+0.22+/-0.12), including unusually large molybdenum ([Mo/Fe]=+0.97+/-0.16) and ruthenium ([Ru/Fe]=+0.69+/-0.17) enhancements. However, this star is not enhanced in carbon ([C/Fe]=-0.06+/-0.19). We analyze an archival near-ultraviolet spectrum of HD94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64 species of 56 elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s- and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99+/-0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutron-capture process (i process), which perhaps operated by the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the i process appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the i process may have been common in the early Galaxy.
We search for low-dimensional chaotic signatures in the optical lightcurve of the $Kepler$ field blazar W2R 1926+42. The frequently used correlation integral method is employed in our analysis. We find no apparent evidence for the presence of low-dimensional chaos in the lightcurve. If further confirmed, these results could be of importance for modeling the blazar emission mechanisms.
In order to understand the formation of the multipolar structures of the pre-planetary nebula (PPN) CRL 618, we perform 3D simulations using a multi-directional bullet model. The optical lobes of CRL 618 and fast molecular outflows at the tips of the lobes have been found to have similar expansion ages of ~ 100 yr. Additional fast molecular outflows were found near the source along the outflow axes with ages of ~ 45 yr, suggesting a second episode of bullet ejections. Thus, in our simulations, two episodes of bullet ejections are assumed. The shaping process is simulated using the ZEUS-3D hydrodynamics code that includes molecular and atomic cooling. In addition, molecular chemistry is also included to calculate the CO intensity maps. Our results show the following: (1) Multi-epoch bullets interacting with the toroidal dense core can produce the collimated multiple lobes as seen in CRL 618. The total mass of the bullets is ~ 0.034 solar mass, consistent with the observed high-velocity CO emission in fast molecular outflows. (2) The simulated CO J=3-2 intensity maps show that the low-velocity cavity wall and the high-velocity outflows along the lobes are reasonably consistent with the observations. The position-velocity diagram of the outflows along the outflow axes shows a linear increase of velocity with distance, similar to the observations. The ejections of these bullets could be due to magneto-rotational explosions or nova-like explosions around a binary companion.
X-rays are a powerful probe of activity in early stages of star formation. They allow us to identify young stars even after they have lost the IR signatures of circumstellar disks and provide constraints on their distance. Here we report on XMM-Newton observations which detect 121 young stellar objects (YSOs) in two fields between L1641S and $\kappa$ Ori. These observations extend the Survey of Orion A with XMM and Spitzer (SOXS). The YSOs are contained in a ring of gas and dust apparent at millimeter wavelengths, and in far-IR and near-IR surveys. The X-ray luminosity function of the young stellar objects detected in the two fields indicates a distance of 250-280 pc, much closer than the Orion A cloud and similar to distance estimates of $\kappa$ Ori. We propose that the ring is a 5-8 pc diameter shell that has been swept up by $\kappa$ Ori. This ring contains several groups of stars detected by Spitzer and WISE including one surrounding the Herbig Ae/Be stars V1818 Ori. In this interpretation, the $\kappa$ Ori ring is one of several shells swept up by massive stars within the Orion Eridanus Superbubble, and is unrelated to the southern portion of Orion A / L1641 S.
Context. Polarimetric observations of Bok globules frequently show a decrease
in the degree of polarization towards their central dense regions (polarization
holes). This behaviour is usually explained with increased disalignment owing
to high density and temperature, or insufficient angular resolution of a
possibly complex magnetic field structure.
Aims. We investigate whether a significant decrease in polarized emission of
dense regions in Bok globules is possible under certain physical conditions.
For instance, we evaluate the impact of optical depth effects and various
properties of the dust phase.
Methods. We use radiative transfer modelling to calculate the temperature
structure of an analytical Bok globule model and simulate the polarized thermal
emission of elongated dust grains. For the alignment of the dust grains, we
consider a magnetic field and include radiative torque and internal alignment.
Results. Besides the usual explanations, selected conditions of the
temperature and density distribution, the dust phase and the magnetic field are
also able to significantly decrease the polarized emission of dense regions in
Bok globules. Taking submm/mm grains and typical column densities of existing
Bok globules into consideration, the optical depth is high enough to decrease
the degree of polarization by up to {\Delta}P~10%. If limited to the densest
regions, dust grain growth to submm/mm size and accumulated graphite grains
decrease the degree of polarization by up to {\Delta}P~10% and {\Delta}P~5%,
respectively. However, the effect of the graphite grains occurs only if they do
not align with the magnetic field.
In this work, we present a study of the central regions of cool-core clusters hosting radio mini-halos, which are di use synchrotron sources extended on cluster-scales surrounding the radio-loud brightest galaxy. We aim to investigate the interplay between the thermal and non-thermal components in the intracluster medium in order to get more insights into these radio sources, whose nature is still unclear. It has recently been proposed that turbulence plays a role for heating the gas in cool cores. A correlation between the radio luminosity of mini-halos, $\nu P_{\nu}$, and the cooling flow power, $P_{\rm CF}$, is expected in the case that this turbulence also plays a role for the acceleration of the relativistic particles. We carried out a homogeneous re-analysis of X-ray Chandra data of the largest sample of cool-core clusters hosting radio mini-halos currently available ($\sim20$ objects), finding a quasi-linear correlation, $\nu P_{\nu} \propto P_{\rm CF}^{0.8}$. We show that the scenario of a common origin of radio mini-halos and gas heating in cool-core clusters is energetically viable, provided that mini-halos trace regions where the magnetic field strength is $B \gg 0.5 \mu G$.
We report the discovery of an off-nuclear ultrasoft hyper-luminous X-ray source candidate 3XMM J141711.1+522541 in the inactive S0 galaxy SDSS J141711.07+522540.8 (z=0.41827, d_L=2.3 Gpc) in the Extended Groth Strip. It is located at a projected offset of ~1.0 (5.2 kpc) from the nucleus of the galaxy and was serendipitously detected in five XMM-Newton observations in 2000 July. Two observations have enough counts and can be fitted with a standard thermal disk with an apparent inner disk temperature kT_MCD ~ 0.13 keV and a 0.28-14.2 keV unabsorbed luminosity L_X ~ 4X10^{43} erg/s in the source rest frame. The source was still detected in three Chandra observations in 2002 August, with similarily ultrasoft but fainter spectra (kT_MCD ~ 0.17 keV, L_X ~ 0.5X10^{43} erg/s). It was not detected in later observations, including two by Chandra in 2005 October, one by XMM-Newton in 2014 January, and two by Chandra in 2014 September-October, implying a long-term flux variation factor of >14. Therefore the source could be a transient with an outburst in 2000-2002. It has a faint optical counterpart candidate, with apparent magnitudes of m_F606W=26.3 AB mag and m_F814W=25.5 AB mag in 2004 December (implying an absolute V-band magnitude of ~-15.9 AB mag). We discuss various explanations for the source and find that it is best explained as a massive black hole (BH) embedded in the nucleus of a possibly stripped satellite galaxy, with the X-ray outburst due to tidal disruption of a surrounding star by the BH. The BH mass is ~10^5 Msun, assuming the peak X-ray luminosity at around the Eddington limit.
We present new near-infrared photometric measurements of the core of the young massive cluster NGC 3603 obtained with extreme adaptive optics. The data were obtained with the SPHERE instrument mounted on ESO Very Large Telescope, and cover three fields in the core of this cluster. We applied a correction for the effect of extinction to our data obtained in the J and K broadband filters and estimated the mass of detected sources inside the field of view of SPHERE/IRDIS, which is 13.5"x13.5". We derived the mass function (MF) slope for each spectral band and field. The MF slope in the core is unusual compared to previous results based on Hubble space telescope (HST) and very large telescope (VLT) observations. The average slope in the core is estimated as -1.06^{+0.26}_{-0.26} for the main sequence stars with 3.5 Msun < M < 120 Msun.Thanks to the SPHERE extreme adaptive optics, 814 low-mass stars were detected to estimate the MF slope for the pre-main sequence stars with 0.6 Msun< M < 3.5 Msun , Gamma = -0.54^{+0.11}_{-0.11} in the K-band images in two fields in the core of the cluster. For the first time, we derive the mass function of the very core of the NGC 3603 young cluster for masses in the range 0.6 - 120 Msun. Previous studies were either limited by crowding, lack of dynamic range, or a combination of both.
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We present chemical evolution models aimed at reproducing the observed (N/O) vs. (O/H) abundance pattern of star forming galaxies in the Local Universe. We derive gas-phase abundances from SDSS spectroscopy and a complementary sample of low-metallicity dwarf galaxies, making use of a consistent set of abundance calibrations. This collection of data clearly confirms the existence of a plateau in the (N/O) ratio at very low metallicity, followed by an increase of this ratio up to high values as the metallicity increases. This trend can be interpreted as due to two main sources of nitrogen in galaxies: i) massive stars, which produce small amounts of pure primary nitrogen and are responsible for the (N/O) ratio in the low metallicity plateau; ii) low- and intermediate-mass stars, which produce both secondary and primary nitrogen and enrich the interstellar medium with a time delay relative to massive stars, and cause the increase of the (N/O) ratio. We find that the length of the low-metallicity plateau is almost solely determined by the star formation efficiency, which regulates the rate of oxygen production by massive stars. We show that, to reproduce the high observed (N/O) ratios at high (O/H), as well as the right slope of the (N/O) vs. (O/H) curve, a differential galactic wind - where oxygen is assumed to be lost more easily than nitrogen - is necessary. No existing set of stellar yields can reproduce the observed trend without assuming differential galactic winds. Finally, considering the current best set of stellar yields, a bottom-heavy initial mass function is favoured to reproduce the data.
We present Hubble WFC3/IR slitless grism spectra of a remarkably bright $z\gtrsim10$ galaxy candidate, GN-z11, identified initially from CANDELS/GOODS-N imaging data. A significant spectroscopic continuum break is detected at $\lambda=1.47\pm0.01~\mu$m. The new grism data, combined with the photometric data, rule out all plausible lower redshift solutions for this source. The only viable solution is that this continuum break is the Ly$\alpha$ break redshifted to ${z_\mathrm{grism}=11.09^{+0.08}_{-0.12}}$, just $\sim$400 Myr after the Big Bang. This observation extends the current spectroscopic frontier by 150 Myr to well before the Planck (instantaneous) cosmic reionization peak at z~8.8, demonstrating that galaxy build-up was well underway early in the reionization epoch at z>10. GN-z11 is remarkably and unexpectedly luminous for a galaxy at such an early time: its UV luminosity is 3x larger than L* measured at z~6-8. The Spitzer IRAC detections up to 4.5 $\mu$m of this galaxy are consistent with a stellar mass of ${\sim10^{9}~M_\odot}$. This spectroscopic redshift measurement suggests that the James Webb Space Telescope (JWST) will be able to similarly and easily confirm such sources at z>10 and characterize their physical properties through detailed spectroscopy. Furthermore, WFIRST, with its wide-field near-IR imaging, would find large numbers of similar galaxies and contribute greatly to JWST's spectroscopy, if it is launched early enough to overlap with JWST.
Cluster star-forming galaxies are found to have an excess of Far-Infrared emission relative to H-alpha (Ha), when compared to those in the field, which could be caused by intense AGN activity, dust and/or declining star formation histories. Here we present spectroscopic observations of Ha emitters in the Cl 0939+4713 (Abell 851) super-cluster at z=0.41, using AF2+WYFFOS on the WHT. We measure [OII], Hbeta (Hb), [OIII], Ha and [NII] for a sample of 119 Ha emitters in and around the cluster. We find that 17+-5% of the Ha emitters are AGN, irrespective of environment. For star-forming galaxies, we obtain Balmer decrements, metallicities and ionisation parameters with different methods, individually and by stacking. We find a strong mass-metallicity relation at all environments, with no significant dependence on environment. The ionisation parameter declines with increasing stellar mass for low-mass galaxies. Ha emitters residing in intermediate environments show the highest ionisation parameters (along with high [OIII]/Ha and high [OIII]/[OII] line ratios, typically twice as large as in the highest and lowest densities), which decline with increasing environmental density. Dust extinction (A$_{H\alpha}$) correlates strongly with stellar mass, but also with environmental density. Star-forming galaxies in the densest environments are found to be significantly dustier (A$_{H\alpha}$~1.5-1.6) than those residing in the lowest density environments (A$_{H\alpha}$~0.6), deviating significantly from what would be predicted given their stellar masses.
Recent observations have revealed the existence of an abundant population of faint, low surface brightness (SB) galaxies, which appear to be numerous and ubiquitous in nearby galaxy clusters, including the Virgo, Coma and Fornax clusters. With median stellar masses of dwarf galaxies, these ultra-diffuse galaxies (UDGs) have unexpectedly large sizes, corresponding to a mean SB of $24\lesssim\langle\mu_e\rangle_r\ {\rm mag}^{-1} {\rm arcsec}^2\lesssim27$ within the effective radius. We show that the UDG population represents the tail of galaxies formed in dwarf-sized haloes with higher-than-average angular momentum at collapse. By adopting the standard model of disk formation -- in which the size of galaxies is set by the spin of the halo -- we recover both the abundance of UDGs as a function of the host cluster mass and the distribution of sizes within the UDG population. According to this model, UDGs are not failed $L_*$ galaxies, but genuine dwarfs, and their low SB is not uniquely connected to the harsh cluster environment. We therefore expect a correspondingly abundant population of UDGs in the field, with likely different morphologies and colours.
We present a new technique for wide and shallow observations using the near-infrared channel of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). Wide-field near-IR surveys with HST are generally inefficient, as guide star acquisitions make it impractical to observe more than one pointing per orbit. This limitation can be circumvented by guiding with gyros alone, which is possible as long as the telescope has three functional gyros. The method presented here allows us to observe mosaics of eight independent WFC3-IR pointings in a single orbit by utilizing the fact that HST drifts by only a very small amount in the 25 seconds between non-destructive reads of unguided exposures. By shifting the reads and treating them as independent exposures the full resolution of WFC3 can be restored. We use this "drift and shift" (DASH) method in the Cycle 23 COSMOS-DASH program, which will obtain 456 WFC3 $H_{160}$ pointings in 57 orbits, covering an area of 0.6 degree$^2$ in the COSMOS field down to $H_{160} = 25$. When completed, the program will more than triple the area of extra-galactic survey fields covered by near-IR imaging at HST resolution. We demonstrate the viability of the method with the first four orbits (32 pointings) of this program. We show that the resolution of the WFC3 camera is preserved, and that structural parameters of galaxies are consistent with those measured in guided observations.
We analyse the sizes, colour gradients, and resolved stellar mass distributions for 36 massive and passive galaxies in the cluster XMMUJ2235-2557 at z=1.39 using optical and near-infrared Hubble Space Telescope imaging. We derive light-weighted S\'ersic fits in five HST bands ($i_{775},z_{850},Y_{105},J_{125},H_{160}$), and find that the size decreases by ~20% going from $i_{775}$ to $H_{160}$ band, consistent with recent studies. We then generate spatially resolved stellar mass maps using an empirical relationship between $M_{*}/L_{H_{160}}$ and $(z_{850}-H_{160})$ and use these to derive mass-weighted S\'ersic fits: the mass-weighted sizes are ~41% smaller than their rest-frame $r$-band counterparts compared with an average of ~12% at z~0. We attribute this evolution to the evolution in the $M_{*}/L_{H_{160}}$ and colour gradient. Indeed, as expected, the ratio of mass-weighted to light-weighted size is correlated with the $M_{*}/L$ gradient, but is also mildly correlated with the mass surface density and mass-weighted size. The colour gradients $(\nabla_{z-H})$ are mostly negative, with a median value of $\sim0.45$ mag dex$^{-1}$, twice the local value. The evolution is caused by an evolution in age gradients along the semi-major axis ($a$), with $\nabla_{age} = d \log(age) / d \log(a)$ $\sim-0.33$, while the survival of weaker colour gradients in old, local galaxies implies that metallicity gradients are also required, with $\nabla_{Z} = d \log(Z) / d \log(a)$ $\sim-0.2$. This is consistent with recent observational evidence for the inside-out growth of passive galaxies at high redshift, and favours a gradual mass growth mechanism, such as minor mergers.
We present the results of CCD UBV observations of the open cluster NGC 6819. We calculated the stellar density profile in the cluster's field to determine the structural parameters of NGC 6819. Using the existing astrometric data, we calculated the probabilities of the stars being physical members of the cluster, and used these objects in the determination of the astrophysical parameters of NGC 6819. We inferred the reddening and metallicity of the cluster as $E(B-V)=0.130\pm0.035$ mag and $[Fe/H]=+0.051\pm 0.020$ dex, respectively, using the U-B vs B-V two-colour diagram and UV excesses of the F-G type main-sequence stars. We fit the colour-magnitude diagrams of NGC6819 with the PARSEC isochrones and derived the distance modula, distance and age of the cluster as $\mu_{V}=12.22\pm 0.10$ mag, $d=2309\pm106$ pc and $t=2.4\pm0.2$ Gyr, respectively. The parameters of the galactic orbit estimated for NGC 6819 indicate that the cluster is orbiting in a slightly eccentric orbit of $e=0.06$ with a period of $P_{orb}=142$ Myr. The slope of the mass function estimated for the cluster is close to the one found for the stars in the solar neighbourhood.
The assembly of the first super massive black holes (SMBHs) at $z \gtrsim 6$ is still a subject of intense debate. If black holes (BHs) grow at their Eddington rate, they must start from $\gtrsim 10^4 \, M_\odot$ seeds formed by the direct collapse of gas. Here we explore the alternative scenario where $\sim 100 \, M_\odot$ BH remnants of the first stars grow at super-Eddington rate via radiatively inefficient slim accretion disks. We use an improved version of the cosmological, data-constrained semi-analytic model GAMETE/QSOdust, where we follow the evolution of nuclear BHs and gas cooling, disk and bulge formation of their host galaxies. Adopting SDSS J1148+5251 (J1148) at $z = 6.4$ as a prototype of luminous $z \gtrsim 6$ quasars, we find that $\sim$ 80% of its SMBH mass is grown by super-Eddington accretion, which can be sustained down to $z \sim 10$ in dense, gas-rich environments. The average BH mass at $z \sim 20$ is $M_{\rm BH} \gtrsim 10^4 \,M_\odot$, comparable to that of direct collapse BHs. At $z = 6.4$ the AGN-driven mass outflow rate is consistent with the observations and the BH-to-bulge mass ratio is compatible with the local scaling relation. However, the stellar mass in the central 2.5 kpc is closer to the value inferred from CO observations. Finally, $\sim 20 %$ of J1148 progenitors at $z=7.1$ have BH luminosities and masses comparable to ULAS J1120+0641, suggesting that this quasar may be one of the progenitors of J1148.
Complex organic molecules (COMs) are detected in many regions of the interstellar medium, including prestellar cores. However, their formation mechanisms in cold (~10 K) cores remain to this date poorly understood. The formyl radical HCO is an important candidate precursor for several O-bearing terrestrial COMs in cores, as an abundant building block of many of these molecules. Several chemical routes have been proposed to account for its formation, both on grain surfaces, as an incompletely hydrogenated product of H addition to frozen-out CO molecules, or in the gas phase, either the product of the reaction between H2CO and a radical, or as a product of dissociative recombination of protonated formaldehyde H2COH+. The detection and abundance determination of H2COH+, if present, could provide clues as to whether this latter scenario might apply. We searched for protonated formaldehyde H2COH+ in the prestellar core L1689B using the IRAM 30m telescope. The H2COH+ ion is unambiguously detected, for the first time in a cold (~10 K) source. The derived abundance agrees with a scenario in which the formation of H2COH+ results from the protonation of formaldehyde. We use this abundance value to constrain the branching ratio of the dissociative recombination of H2COH+ towards the HCO channel to ~10-30%. This value could however be smaller if HCO can be efficiently formed from gas-phase neutral-neutral reactions, and we stress the need for laboratory measurements of the rate constants of these reactions at 10 K. Given the experimental difficulties in measuring branching ratios experimentally, observations can bring valuable constraints on these values, and provide a useful input for chemical networks.
It is still unknown how magnetic field-generation mechanisms could operate in low-mass dwarf galaxies. Here, we present a detailed study of a nearby pure-disk dwarf galaxy NGC 2976. Unlike previously observed dwarf objects, this galaxy possesses a clearly defined disk. For the purpose of our studies, we performed deep multi-frequency polarimetric observations of NGC 2976 with the VLA and Effelsberg radio telescopes. Additionally, we supplement them with re-imaged data from the WSRT-SINGS survey. The magnetic field morphology discovered in NGC 2976 consists of a southern polarized ridge. This structure does not seem to be due to just a pure large-scale dynamo process (possibly cosmic-ray driven) at work in this object, as indicated by the RM data and dynamo number calculations. Instead, the field of NGC 2976 is modified by past gravitational interactions and possibly also by ram pressure inside the M 81 galaxy group environment. The estimates of total (7 muG) and ordered (3 muG) magnetic field strengths, as well as degree of field order (0.46), which is similar to those observed in spirals, suggest that tidally generated magnetized gas flows can further enhance dynamo action in the object. NGC 2976 is apparently a good candidate for the efficient magnetization of its neighbourhood. It is able to provide an ordered (perhaps also regular) magnetic field into the intergalactic space up to a distance of about 5 kpc. Tidal interactions (and possibly also ram pressure) can lead to the formation of unusual magnetic field morphologies (like polarized ridges) in galaxies out of the star-forming disks, which do not follow any observed component of the interstellar medium (ISM), as observed in NGC 2976. These galaxies are able to provide ordered magnetic fields far out of their main disks.
We present deep new GTC/OSIRIS narrow-band images and optical WHT/ISIS long-slit spectroscopy of the merging system Mrk273 that show a spectacular extended halo of warm ionised gas out to a radius of $\sim45$ kpc from the system nucleus. Outside of the immediate nuclear regions (r > 6 kpc), there is no evidence for kinematic disturbance in the ionised gas: in the extended regions covered by our spectroscopic slits the emission lines are relatively narrow (FWHM $\lesssim$ 350 km$\rm s^{-1}$) and velocity shifts small (|$\Delta$V| $\lesssim{} $250 km$\rm s^{-1}$). This is despite the presence of powerful near-nuclear outflows (FWHM > 1000 km$\rm s^{-1}$; |$\Delta$V| > 400 km$\rm s^{-1}$; r < 6 kpc). Diagnostic ratio plots are fully consistent with Seyfert 2 photo-ionisation to the NE of the nuclear region, however to the SW the plots are more consistent with low-velocity radiative shock models. The kinematics of the ionised gas, combined with the fact that the main structures are aligned with low-surface-brightness tidal continuum features, are consistent with the idea that the ionised halo represents tidal debris left over from a possible triple-merger event, rather than a reservoir of outflowing gas.
Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN) recently identified as a new class of $\gamma$-ray sources. The high energy emission is explained by the presence of a relativistic jet observed at small angles, just like in the case of blazars. When the latter are observed at larger angles they appear as radio-galaxies, but an analogue parent population for beamed NLS1s has not yet been determined. In this work we analyze this problem by studying the physical properties of three different samples of parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s, and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In our approach, we first derived black hole mass and Eddington ratio from the optical spectra, then we investigated the interaction between the jet and the narrow-line region from the [O III] $\lambda\lambda$4959,5007 lines. Finally, the radio luminosity function allowed us to compare their jet luminosity and hence determine the relations between the samples.
We examine FUV images of the LITTLE THINGS sample of nearby dwarf irregular (dIrr) and Blue Compact Dwarf (BCD) galaxies to identify distinct young regions in their far outer disks. We use these data, obtained with the Galaxy Evolution Explorer satellite, to determine the furthest radius at which in situ star formation can currently be identified. The FUV knots are found at distances from the center of the galaxies of 1 to 8 disk scale lengths and have ages of <20 Myrs and masses of 20 to 1E5 Msolar. The presence of young clusters and OB associations in the outer disks of dwarf galaxies shows that dIrrs do have star formation taking place there in spite of the extreme nature of the environment. Most regions are found where the HI surface density is ~1 Msolar per pc2, although both the HI and dispersed old stars go out much further. This limiting density suggests a cutoff in the ability to form distinct OB associations and perhaps even stars. We compare the star formation rates in the FUV regions to the average rates expected at their radii and beyond from the observed gas, using the conventional correlation for gas-rich regions. The localized rates are typically 10% of the expected average rates for the outer disks. Either star formation in dIrrs at surface densities <1 Msolar per pc2 occurs without forming distinct associations, or the Kennicutt-Schmidt relation over-predicts the rate beyond this point. In the latter case, the stellar disks in the far-outer parts of dIrrs result from scattering of stars from the inner disk.
We present a strong and weak gravitational lens model of the galaxy cluster MACSJ0416.1-2403, constrained using spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS) and Hubble Frontier Fields (HFF) imaging data. We search for emission lines in known multiply imaged sources in the GLASS spectra, obtaining secure spectroscopic redshifts of 31 multiple images belonging to 16 distinct source galaxies. The GLASS spectra provide the first spectroscopic measurements for 6 of the source galaxies. The weak lensing signal is acquired from 884 galaxies in the F606W HFF image. By combining the weak lensing constraints with 15 multiple image systems with spectroscopic redshifts and 9 multiple image systems with photometric redshifts, we reconstruct the gravitational potential of the cluster on an adaptive grid. The resulting total mass density map is compared with a stellar mass density map obtained from the deep Spitzer Frontier Fields imaging data to study the relative distribution of stellar and total mass in the cluster. We find that the projected stellar mass to total mass ratio, $f_{\star}$, varies considerably with the stellar surface mass density. The mean projected stellar mass to total mass ratio is $\langle f_{\star} \rangle= 0.009 \pm 0.003 $ (stat.), but with a systematic error as large as $0.004-0.005$, dominated by the choice of the IMF. We find agreement with several recent measurements of $f_{\star}$ in massive cluster environments. The lensing maps of convergence, shear, and magnification are made available to the broader community in the standard HFF format.
The cold dark matter model of structure formation faces apparent problems on
galactic scales. Several threads point to excessive halo concentration,
including central densities that rise too steeply with decreasing radius. Yet,
random fluctuations in the gaseous component can 'heat' the centres of haloes,
decreasing their densities. We present a theoretical model deriving this effect
from first principles: stochastic variations in the gas density are converted
into potential fluctuations that act on the dark matter; the associated force
correlation function is calculated and the corresponding stochastic equation
solved. Assuming a power law spectrum of fluctuations with maximal and minimal
cutoff scales, we derive the velocity dispersion imparted to the halo particles
and the relevant relaxation time. We further perform numerical simulations,
with fluctuations realised as a Gaussian random field, which confirm the
formation of a core within a timescale comparable to that derived analytically.
Non-radial collective modes enhance the energy transport process that erases
the cusp, though the parametrisations of the analytical model persist.
In our model, the dominant contribution to the dynamical coupling driving the
cusp-core transformation comes from the largest scale fluctuations. Yet, the
efficiency of the transformation is independent of the value of the largest
scale and depends weakly (linearly) on the power law exponent; it effectively
depends on two parameters: the gas mass fraction and the normalisation of the
power spectrum. This suggests that cusp-core transformations observed in
hydrodynamic simulations of galaxy formation may be understood and parametrised
in simple terms, the physical and numerical complexities of the various
implementations notwithstanding.
We present a renewed look at M31's Giant Stellar Stream along with the nearby structures Stream C and Stream D, exploiting a new algorithm capable of fitting to the red giant branch (RGB) of a structure in both colour and magnitude space. Using this algorithm, we are able to generate probability distributions in distance, metallicity and RGB width for a series of subfields spanning these structures. Specifically, we confirm a distance gradient of approximately 20 kpc per degree along a 6 degree extension of the Giant Stellar Stream, with the farthest subfields from M31 lying ~ 120 kpc more distant than the inner-most subfields. Further, we find a metallicity that steadily increases from -0.7^{+0.1}_{-0.1} dex to -0.2^{+0.2}_{-0.1} dex along the inner half of the stream before steadily dropping to a value of -1.0^{+0.2}_{-0.2} dex at the farthest reaches of our coverage. The RGB width is found to increase rapidly from 0.4^{+0.1}_{-0.1} dex to 1.1^{+0.2}_{-0.1} dex in the inner portion of the stream before plateauing and decreasing marginally in the outer subfields of the stream. In addition, we estimate Stream C to lie at a distance between 794 and 862 kpc and Stream D between 758 kpc and 868 kpc. We estimate the median metallicity of Stream C to lie in the range -0.7 to -1.6 dex and a metallicity of -1.1^{+0.3}_{-0.2} dex for Stream D. RGB widths for the two structures are estimated to lie in the range 0.4 to 1.2 dex and 0.3 to 0.7 dex respectively. In total, measurements are obtained for 19 subfields along the Giant Stellar Stream, 4 along Stream C, 5 along Stream D and 3 general M31 spheroid fields for comparison. We thus provide a higher resolution coverage of the structures in these parameters than has previously been available in the literature.
Based on the swing amplification model of Julian and Toomre (1966), we investigate the formation and structure of stellar spirals in disk galaxies. We calculate the pitch angle, wavelengths, and amplification factor of the most amplified mode. We also obtain the fitting formulae of these quantities as a function of the epicycle frequency and Toomre's $Q$. As the epicycle frequency increases, the pitch angle and radial wavelength increases, while the azimuthal wavelength decreases. The pitch angle and radial wavelength increases with $Q$, while the azimuthal wavelength weakly depends on $Q$. The amplification factor decreases with $Q$ rapidly. In order to confirm the swing amplification model, we perform local $N$-body simulations. The wavelengths and pitch angle by the swing amplification model are in good agreement with those by $N$-body simulations. The dependence of the amplification factor on the epicycle frequency in $N$-body simulations is generally consistent with that in the swing amplification model. Using these results, we estimate the number of spiral arms as a function of the shear rate. The number of spiral arms increases with the shear rate if the disk to halo mass ratio is fixed.
We have identified the four most significant features in the $UV$ velocity distribution of solar neighborhood stars: H1, H2 in the Hercules stream and W1, W2 in the Wolf 630 stream. We have formulated the problem of determining several characteristics of the central Galactic bar independently from each of the identified features by assuming that the Hercules and Wolf 630 streams are of a bar-induced dynamical nature. The problem has been solved by constructing 2:1 resonant orbits in the rotating bar frame for each star in these streams. Analysis of the resonant orbits found has shown that the bar pattern speed is 45-55 km/s/kpc, while the bar angle lies within the range 40-60 degrees. The results obtained are consistent with the view that the Hercules and Wolf 630 streams could be formed by a long-term influence of the Galactic bar leading to a characteristic bimodal splitting of the UV velocity plane.
Based on data aquired in 13 orbits of HST time, we present a detailed evolutionary history of the M31 dSph satellite Andromeda XVI, including its life-time star formation history, the spatial distribution of its stellar populations, and the properties of its variable stars. And XVI is characterized by prolonged star formation activity from the oldest epochs until star formation was quenched ~6 Gyr ago, and, notably, only half of the mass in stars of And XVI was in place 10 Gyr ago. And XVI appears to be a low mass galaxy for which the early quenching by either reionization or starburst feedback seems highly unlikely, and thus, is most likely due to an environmental effect (e.g., an interaction), possibly connected to a late infall in the densest regions of the Local Group. Studying the star formation history as a function of galactocentric radius, we detect a mild gradient in the star formation history: the star formation activity between 6 and 8 Gyr ago is significantly stronger in the central regions than in the external regions, although the quenching age appears to be the same, within 1 Gyr. We also report the discovery of 9 RR Lyrae stars, 8 of which belong to And XVI. The RR Lyrae stars allow a new estimate of the distance, (m-M)0= 23.72+/-0.09 mag, which is marginally larger than previous estimates based on the tip of the red giant branch.
Open clusters (OCs) are crucial for studying the formation and evolution of the Galactic disc. However, the lack of a large number of OCs analyzed homogeneously hampers the investigations about chemical patterns and the existence of Galactocentric radial and vertical gradients, or an age-metallicity relation. To overcome this, we have designed the Open Cluster Chemical Abundances from Spanish Observatories survey (OCCASO). We aim to provide homogeneous radial velocities, physical parameters and individual chemical abundances of six or more Red Clump stars for a sample of 25 old and intermediate-age OCs visible from the Northern hemisphere. To do so, we use high resolution spectroscopic facilities (R> 62,000) available at Spanish observatories. We present the motivation, design and current status of the survey, together with the first data release of radial velocities for 77 stars in 12 OCs, which represents about 50% of the survey. We include clusters never studied with high-resolution spectroscopy before (NGC~1907, NGC~6991, NGC~7762), and clusters in common with other large spectroscopic surveys like the Gaia-ESO Survey (NGC~6705) and APOGEE (NGC~2682 and NGC~6819). We perform internal comparisons between instruments to evaluate and correct internal systematics of the results, and compare our radial velocities with previous determinations in the literature, when available. Finally, radial velocities for each cluster are used to perform a preliminar kinematic study in relation with the Galactic disc.
The grand-design face-on spiral galaxy NGC6946 is remarkable because of its high star formation activity, the massive northern spiral arm, and the magnetic arms, which are observed in polarized radio synchrotron emission and are located between the optical arms and possibly are magnetic reconnection regions. X-ray observations of NGC6946 performed with XMM-Newton were used to study the emission from X-ray point sources and diffuse hot gas, including the magnetic arms and the halo. Spectral fitting of the diffuse X-ray emission allowed us to derive temperatures of the hot gas. With assumptions about the emission volume, this allowed us to estimate gas densities, masses, and cooling times. To explain the X-ray emission from the spiral arms of NGC6946 two-temperature plasma models are needed to account for the disk and halo emission. The interarm regions show only one thermal component. We observe that the temperature of the hot gas in and above the magnetic arm regions increases slightly when compared to the average temperatures in the areas in and above the spiral arms. For the southwestern part of the disk, which is depolarized in the radio range by Faraday rotation, we find more efficient mixing of disk and halo gas. We propose magnetic reconnection in the magnetic arm regions of NGC6946 as the possible cause of the additional heating of the gas and ordering of the magnetic fields. In the southwestern part of the galactic disk we observed indications of a possible faster outflow of the hot gas. A very hot gas within the MF16 nebula possibly suggests shock heating by a supernova explosion.
We report serendipitous detections of line emission with the Atacama Large Millimeter/submillimeter Array (ALMA) in band 3, 6, and 7 in the central parsec down to within 1" around Sgr A* at an up to now highest resolution (<0.5") view of the Galactic Center (GC) in the sub-millimeter (sub-mm) domain. From the 100 GHz continuum and the H39\alpha emission we obtain a uniform electron temperature around 6000 K for the minispiral. The spectral index of Sgr A* is ~ 0.5 at 100 - 250 GHz and ~ 0.0 at 230 - 340 GHz. The bright sources in the center show spectral indices around -0.1 implying Bremsstrahlung emission, while dust emission is emerging in the minispiral exterior. Apart from CS, which is most widespread in the center, also H13CO+, HC3N, SiO, SO, C2H, CH3OH, 13CS and N2H+ are detected. The bulk of the clumpy emission regions is at positive velocities and in a region confined by the minispiral Northern Arm, Bar and the sources IRS 3 and 7. Though partly spatially overlapping with the radio recombination line (RRL) emission at same negative velocities, the relation to the minispiral remains unclear. A likely explanation is an infalling clump consisting of denser cloud cores embedded in diffuse gas. The central association of clouds shows three times higher CS/X (X: any other observed molecule) ratios than the circumnuclear disk (CND) suggesting a combination of higher excitation - by a temperature gradient and/or IR-pumping - and abundance enhancement due to UV- and/or X-ray emission. Hence, we conclude that this central association is closer to the center than the CND. Moreover, we find molecular emission at velocities up to 200 km s-1. ...
The population of supermassive black holes (SMBHs) is composed by quiescent SMBHs, such as those seen in local galaxies including the Milky Way's, and active ones, resulting in quasars and active galactic nuclei (AGN). Outside our neighbourhood, all the information we have on SMBHs is derived from quasars and AGN, giving us a partial view. We study the evolution of the SMBH population, total and active, by the continuity equation, backwards in time from z=0 to z=4. Type-1 and type-2 AGN are differentiated in the model on the basis of the Eddington ratio distribution, chosen on the basis of observational estimates. The duty cycle is obtained by matching the luminosity function of quasars, and the average radiative efficiency is the only free parameter in the model. For higher radiative efficiencies (>~0.07) a large fraction of the SMBH population, most of them quiescent, must already be in place by z=4. For lower radiative efficiencies (~0.05), the duty cycle increases with the redshift and the SMBH population evolves dramatically since z=4. The mass function of active SMBHs does not depend on the choice of the radiative efficiency or of the local SMBH mass function, but it is mainly determined by the quasar luminosity function, once the Eddington ratio distribution is fixed. Only a direct measurement of the total BHMF at redshifts z>~2 could break these degeneracies giving important constraints on the average radiative efficiency. Focusing on type-1 AGN, for which observational estimates of the mass function and Eddington ratio distribution exist at various redshift, models with lower radiative efficiencies reproduce better the high-mass end of the mass function at high-z, but they tend to over-predict it at low-z, and vice-versa for models with higher radiative efficiencies.
We introduce a new algorithm for colour separation and deblending of multi-band astronomical images called MuSCADeT which is based on Morpho-spectral Component Analysis of multi-band images. The MuSCADeT algorithm takes advantage of the sparsity of astronomical objects in morphological dictionaries such as wavelets and their differences in spectral energy distribution (SED) across multi-band observations. This allows us to devise a model independent and automated approach to separate objects with different colours. We show with simulations that we are able to separate highly blended objects and that our algorithm is robust against SED variations of objects across the field of view. To confront our algorithm with real data, we use HST images of the strong lensing galaxy cluster MACS J1149+2223 and we show that MuSCADeT performs better than traditional profile-fitting techniques in deblending the foreground lensing galaxies from background lensed galaxies. Although the main driver for our work is the deblending of strong gravitational lenses, our method is fit to be used for any purpose related to deblending of objects in astronomical images. An example of such an application is the separation of the red and blue stellar populations of a spiral galaxy in the galaxy cluster Abell 2744. We provide a python package along with all simulations and routines used in this paper to contribute to reproducible research efforts. Codes can be found at this http URL
We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] < -3.0) star, SDSS J134338.67+484426.6, identified during the course of the MARVELS spectroscopic pre-survey of some 20000 stars to identify suitable candidates for exoplanet searches. This star, with an apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and is one of only ~20 known EMP stars that are this bright or brighter. Our high-resolution spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42, having "normal" carbon and no enhancement of neutron-capture abundances. Strontium is under-abundant, [Sr/Fe] =-0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs to the sparsely populated class of alpha-poor EMP stars that exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar metallicity. The observed variations in radial velocity from several epochs of (low- and high-resolution) spectroscopic follow-up indicate that SDSS J134338.67+484426.6 is a possible long-period binary. We also discuss the abundance trends in EMP stars for r-process elements, and compare with other magnesium-poor stars.
The census of solar neighbours is still complemented by new discoveries, mainly of very low-mass, faint dwarfs, close to or within the substellar domain. These discoveries contribute to a better understanding of the field population; its origin in terms of Galactic dynamics and (sub)stellar formation and evolution. Also, the nearest stars and brown dwarfs at any given age allow the most precise direct characterization, including the search for planetary companions. We aim to further assess the substellar census on the Galactic plane. We projected the 136 stars and 26 brown dwarfs known at <6.5 pc on the Galactic plane and evaluated their distributions. Stars present a uniform- and brown dwarfs a non-uniform distribution, with 21 objects behind the Sun and only five ahead relative to the direction of rotation of the Galaxy. This substellar configuration has a probability of 0.098$^{+10.878}_{-0.098}$% relative to uniformity. The helio- and geocentric nature of the distribution suggests it might result in part from an observational bias, which if compensated for by future discoveries, might increase the brown-dwarf-to-star ratio, shifting it closer to values found in some star forming regions.
During the asymptoyic giant branch (AGB) phase, different elements are dredge-up to the stellar surface depending on progenitor mass and metallicity. When the mass loss increases at the end of the AGB, a circumstellar dust shell is formed, where different (C-rich or O-rich) molecules and solid-state compounds are formed. These are further processed in the transition phase between AGB stars and planetary nebulae (PNe) to create more complex organic molecules and inorganic solid-state compounds (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene precursors in C-rich environments and oxides and crystalline silicates in O-rich ones). We present an observational review of the different molecules and solid-state materials that are formed from the AGB to the PN phases. We focus on the formation routes of complex fullerene (and fullerene-based) molecules as well as on the level of dust processing depending on metallicity.
We explore the formation of superbubbles through energy deposition by multiple supernovae (SNe) in a uniform medium. We use total energy conserving, 3-D hydrodynamic simulations to study how SNe correlated in space and time create superbubbles. While isolated SNe fizzle out completely by $\sim 1$ Myr due to radiative losses, for a realistic cluster size it is likely that subsequent SNe go off within the hot/dilute bubble and sustain the shock till the cluster lifetime. We scan the parameter space of ISM density ($n_{g0}$), number of SNe ($N_{\rm OB}$), and star cluster radius ($r_{\rm cl}$) to study the conditions for the formation of an overpressured (super)bubble. For realistic cluster sizes, we find that the bubble remains overpressured only if, for a given $n_{g0}$, $N_{\rm OB}$ is sufficiently large. While most of the input energy is still lost radiatively, superbubbles can retain up to $\sim 5-10\%$ of the input energy in form of kinetic+thermal energy till 10 Myr for ISM density $n_{g0} \approx 1$ cm$^{-3}$. We find that the mechanical efficiency decreases for higher densities ($\eta_{\rm mech} \propto n_{g0}^{-2/3}$). We compare the radii and velocities of simulated supershells with observations and the classical adiabatic model. Our simulations show that the superbubbles retain only $\lesssim 10\%$ of the injected energy, thereby explaining the observed smaller size and slower expansion of supershells. We also confirm that a sufficiently large ($\gtrsim 10^4$) number of SNe is required to go off in order to create a steady wind with a stable termination shock within the superbubble.
We present the results of an optical photometry and high-resolution spectroscopy campaign for a modest sample of X-ray selected stars in the Chamaeleon and Rho Ophiuchus star forming regions. With R~50000 optical spectra, we establish kinematic membership of the parent association and confirm stellar youth for each star in our sample. With the acquisition of new standardized BVIc photometry, in concert with near-infrared data from the literature, we derive age and mass from stellar positions in model-dependent Hertzsprung-Russell diagrams. We compare isochronal ages derived using colour-dependent extinction values finding that, within error bars, ages are the same irrespective of whether E(B-V), E(V-Ic), E(J-H) or E(H-K) is used to establish extinction, although model ages tend to be marginally younger for redder Ecolour values. For Cham I and Eta Cham members we derive ages of ~< 5-6 Myr, whereas our three Eta Cha candidates are more consistent with a ~> 25 Myr post-T Tauri star population. In Rho Ophiuchus, most stars in our sample have isochronal ages <10 Myr. Five objects show evidence of strong infrared excess (Av>5) in the 2MASS colour colour diagram, however in terms of Halpha emission, all stars except RXJ1625.6-2613 are consistent with being weak-lined T-Tauri stars. Spectral energy distributions (SEDs) over the range ~ 4000A < wavelength < 1000 microns, show that only one Chamaeleon star (RXJ1112.7-7637) and three Rho Ophiuchus stars (ROXR1 13, RXJ1625.6-2613 & RXJ1627.1-2419) reveal substantial departures from a bare photosphere.
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The aim of this paper is to characterize the radial structure of the star formation rate (SFR) in galaxies in the nearby Universe as represented by the CALIFA survey. The sample under study contains 416 galaxies observed with IFS, covering a wide range of Hubble types and stellar masses. Spectral synthesis techniques are applied to obtain radial profiles of the intensity of the star formation rate in the recent past, and the local sSFR. To emphasize the behavior of these properties for galaxies that are on and off the main sequence of star formation (MSSF) we stack the individual radial profiles in bins of galaxy morphology and stellar masses. Our main results are: a) The intensity of SFR shows declining profiles that exhibit very little differences between spirals. The dispersion between the profiles is significantly smaller in late type spirals. This confirms that the MSSF is a sequence of galaxies with nearly constant intensity of SFR b) sSFR values scale with Hubble type and increase radially outwards, with a steeper slope in the inner 1 HLR. This behavior suggests that galaxies are quenched inside-out, and that this process is faster in the central, bulge-dominated part than in the disks. c) As a whole, and at all radii, E and S0 are off the MSSF. d) Applying the volume-corrections for the CALIFA sample, we obtain a density of star formation in the local Universe of 0.0105 Msun/yr/Mpc^{-3}. Most of the star formation is occurring in the disks of spirals. e) The volume averaged birthrate parameter, b'=0.39, suggests that the present day Universe is forming stars at 1/3 of its past average rate. E, S0, and the bulge of early type spirals contribute little to the recent SFR of the Universe, which is dominated by the disks of later spirals. f) There is a tight relation between the intensity of the SFR and stellar mass, defining a local MSSF relation with a logarithmic slope of 0.8.
Many recent observations and numerical simulations suggest that nearby massive, early-type galaxies were formed through a "two-phase" process. In the proposed second phase, the extended stellar envelope was accumulated through many dry mergers. However, details of the past merger history of present-day ellipticals, such as the typical merger mass ratio, are difficult to constrain observationally. Within the context and assumptions of the two-phase formation scenario, we propose a straightforward method, using photometric data alone, to estimate the average mass ratio of mergers that contributed to the build-up of massive elliptical galaxies. We study a sample of nearby massive elliptical galaxies selected from the Carnegie-Irvine Galaxy Survey, using two-dimensional analysis to decompose their light distribution into an inner, denser component plus an extended, outer envelope, each having a different optical color. The combination of these two substructures accurately recovers the negative color gradient exhibited by the galaxy as whole. The color difference between the two components (<\Delta(B-V)> ~ 0.10 mag; <\Delta(B-R)> ~ 0.14 mag), based on the slope of the M_stellar-color relation for nearby early-type galaxies, can be translated into an estimate of the average mass ratio of the mergers. The rough estimate, 1:5 to 1:10, is consistent with the expectation of the two-phase formation scenario, suggesting that minor mergers were largely responsible for building up to the outer stellar envelope of present-day massive ellipticals. With the help of accurate photometry, large sample size, and more choices of colors promised by ongoing and future surveys, the approach proposed here can reveal more insights into the growth of massive galaxies during the last few Gyr.
Two-body interactions play a major role in shaping the structural and dynamical properties of globular clusters (GCs) over their long-term evolution. In particular, GCs evolve toward a state of partial energy equipartition that induces a mass-dependence in their kinematics. By using a set of Monte Carlo cluster simulations evolved in quasi-isolation, we show that the stellar mass dependence of the velocity dispersion $\sigma(m)$ can be described by an exponential function $\sigma^2\propto \exp(-m/m_\mathrm{eq})$, with the parameter $m_\mathrm{eq}$ quantifying the degree of partial energy equipartition of the systems. This simple parametrization successfully captures the behaviour of the velocity dispersion at lower as well as higher stellar masses, that is, the regime where the system is expected to approach full equipartition. We find a tight correlation between the degree of equipartition reached by a GC and its dynamical state, indicating that clusters that are more than about 20 core relaxation times old, have reached a maximum degree of equipartition. This equipartition$-$dynamical state relation can be used as a tool to characterize the relaxation condition of a cluster with a kinematic measure of the $m_\mathrm{eq}$ parameter. Vice versa, the mass-dependence of the kinematics can be predicted knowing the relaxation time solely on the basis of photometric measurements. Moreover, any deviations from this tight relation could be used as a probe of a peculiar dynamical history of a cluster. Finally, our novel approach is important for the interpretation of state-of-the-art Hubble Space Telescope proper motion data, for which the mass dependence of kinematics can now be measured, and for the application of modeling techniques which take into consideration multi-mass components and mass segregation.
Recent theoretical studies with N-body simulations predict that large numbers of stellar black holes (BHs) could remain bound to some globular clusters (GCs) at present, and merging BH--BH binaries are produced dynamically in significant numbers. Here we systematically vary model assumptions within existing uncertainties and study their effects on the evolution of BHs in GCs and the final structural properties of GCs. We use a parallel Monte Carlo code, which provides much higher computational speed than direct N-body codes, thereby allowing large numbers of models to be computed. We find that variations in initial assumptions can set otherwise identical initial clusters on completely different evolutionary paths, significantly affecting their observable properties at present, or even affecting the cluster's very survival to the present. However, these changes usually do not affect the numbers or properties of merging BH--BH binaries produced by GCs. The only exception is that varying assumptions about stellar IMF and winds can significantly change the numbers and masses of BHs in merging binaries. For a given IMF and metallicity, all other variations (e.g., in initial binary properties and binary fraction) leave the numbers and masses of BH--BH mergers largely unchanged. This is in contrast to binary population synthesis models for the field, where results are sensitive to a large number of uncertain parameters in the initial properties of binaries and in the binary stellar evolution physics. We discuss our results in the context of the recently detected BH--BH merger GW150914, assuming that it originated in a GC. The large BH masses in this system are likely not common, even with weak winds and low metallicity; instead, the properties inferred for the other LIGO trigger event, LVT151012, are closer to what we would predict for the bulk of BH--BH mergers produced dynamically in GCs.
We present the first ab initio cosmological simulations of a CR7-like object which approximately reproduce the observed line widths and strengths. In our model, CR7 is powered by a massive (2.23 x 10^7 M_Sun), accreting (0.25 Eddington) supermassive black hole (BH). Our model takes into account multi-dimensional effects, X-ray feedback, secondary ionizations and primordial chemistry. We estimate Ly-alpha line widths by post-processing simulation output with Monte Carlo radiative transfer and calculate emissivity contributions from radiative recombination and collisional excitation. We find the luminosities in the Lyman-alpha and He II 1640 angstrom lines to be 5.0 x 10^44 and 2.4 x 10^43 erg/s, respectively, in agreement with the observed values of > 8.3 x 10^43 and 2.0 x 10^43 erg/s. We also find that the black hole heats the halo and renders it unable to produce stars as required to keep the halo metal free. These results demonstrate the viability of the BH hypothesis for CR7 in a cosmological context. Assuming the BH mass and accretion rate that we find, we estimate the synchrotron luminosity of CR7 to be P ~ 10^40 - 10^41 erg/s, which is sufficiently luminous to be observed in muJy observations and would discriminate this scenario from one where the luminosity is driven by Population III stars.
We present the first results from our X-ray study of young radio sources classified as Compact Symmetric Objects (CSOs). Using the Chandra X-ray Observatory we observed six CSOs for the first time in X-rays, and re-observed four CSOs with previous XMM-Newton or Beppo-SAX data. We also included six other CSOs with the archival data to built a pilot sample of the 16 CSO sources observed in X-rays to date. All the sources are nearby, $z<1$, and the age of their radio structures, $<3000$ years, has been derived from the hotspots advance velocity. Our results show heterogeneous nature of the CSOs X-ray emission indicating a complex environment associated with young radio sources. The sample covers a range in X-ray luminosity, $L_{2-10 \rm keV} \sim 10^{41}$-$10^{45}$ erg s$^{-1}$, and intrinsic absorbing column density of $N_H \simeq 10^{21}$-10$^{22}$ cm$^{-2}$. In particular, we detected extended X-ray emission in 1718$-$649, a hard photon index of $\Gamma = 0.8^{+0.3}_{-0.2}$ in 2021$+$614 consistent with either a Compton thick absorber or non-thermal emission from compact radio lobes; an ionized iron emission line, $E_{rest}=(6.62\pm0.04)$ keV, $EW=154^{+65}_{-58}$ eV (for a power law and a Gaussian line model), in 0710$+$439; and the 2-10 keV X-ray flux decrease by an order of magnitude since the 2008 XMM-Newton observation in 1607$+$26. We conclude that our pilot study of CSOs provides a variety of exceptional diagnostics and highlights the importance of deep X-ray observations of large samples of young sources. This is necessary in order to constrain theoretical models for the earliest stage of radio source evolution and study the interactions of young radio sources with the interstellar environment of their host galaxies.
The central regions of galaxies show the presence of super massive black holes and/or very dense stellar clusters. Both such objects seem to follow similar host-galaxy correlations, suggesting that they are members of the same family of Compact Massive Objects. Here we investigate a huge data collection of Compact Massive Objects properties to correlate them with absolute magnitude, velocity dispersion and mass of their host galaxies. We draw also some preliminary astrophysical conclusions.
We present measurements of the [NII]/Ha ratio as a probe of gas-phase oxygen abundance for a sample of 419 star-forming galaxies at z=0.6-2.7 from the KMOS3D near-IR multi-IFU survey. The mass-metallicity relation (MZR) is determined consistently with the same sample selection, metallicity tracer, and methodology over the wide redshift range probed by the survey. We find good agreement with long-slit surveys in the literature, except for the low-mass slope of the relation at z~2.3, where this sample is less biased than previous samples based on optical spectroscopic redshifts. In this regime we measure a steeper slope than some literature results. Excluding the AGN contribution from the MZR reduces sensitivity at the high mass end, but produces otherwise consistent results. There is no significant dependence of the [NII]/Ha ratio on SFR or environment at fixed redshift and stellar mass. The IFU data allow spatially resolved measurements of [NII]/Ha, from which we can infer abundance gradients for 180 galaxies, thus tripling the current sample in the literature. The observed gradients are on average flat, with only 15 gradients statistically offset from zero at >3sigma. We have modelled the effect of beam-smearing, assuming a smooth intrinsic radial gradient and known seeing, inclination and effective radius for each galaxy. Our seeing-limited observations can recover up to 70% of the intrinsic gradient for the largest, face-on disks, but only 30% for the smaller, more inclined galaxies. We do not find significant trends between observed or corrected gradients and any stellar population, dynamical or structural galaxy parameters, mostly in agreement with existing studies with much smaller sample sizes. In cosmological simulations, strong feedback is generally required to produce flat gradients at high redshift.
Observations of 28SiO v=0 J=1-0 line emission (7-mm wavelength) from AGB
stars show in some cases peculiar profiles, composed of a central intense
component plus a wider plateau. Very similar profiles have been observed in CO
lines from some AGB stars and most post-AGB nebulae and, in these cases, they
are clearly associated with the presence of conspicuous axial symmetry and
bipolar dynamics.
We present systematic observations of 28SiO v=0 J=1-0 emission in 28 evolved
stars, performed with the 40~m radio telescope of the IGN in Yebes, Spain. We
find that the composite core plus plateau profiles are almost always present in
O-rich Miras, OH/IR stars, and red supergiants. They are also found in one
S-type Mira ($\chi$ Cyg), as well as in two semiregular variables (X Her and RS
Cnc) that are known to show axial symmetry. In the other objects, the profiles
are simpler and similar to those of other molecular lines. The composite
structure appears in the objects in which SiO emission is thought to come from
the very inner circumstellar layers, prior to dust formation. The central
spectral feature is found to be systematically composed of a number of narrow
spikes, except for X Her and RS Cnc, in which it shows a smooth shape that is
very similar to that observed in CO emission. These spikes show a significant
(and mostly chaotic) time variation, while in all cases the smooth components
remain constant within the uncertainties. The profile shape could come from the
superposition of standard wide profiles and a group of weak maser spikes.
Alternatively, we speculate that the very similar profiles detected in objects
that are axisymmetric may be indicative of the systematic presence of a
significant axial symmetry in the very inner circumstellar shells around AGB
stars; the presence of such symmetry would be independent of the probable weak
maser effects in the central spikes.
HESS J1943+213 is an unidentified TeV source that is likely a high-frequency-peaked BL Lac (HBL) object but also compatible with a pulsar wind nebula (PWN) nature. Each of these enormously different astronomical interpretations is supported by some of the observed unusual characteristics. In order to finally classify and understand this object we took a three-pronged approach, through time-domain, high angular resolution, and multi-frequency radio studies. First, our deep time-domain observations with the Arecibo telescope failed to uncover the putative pulsar powering the proposed PWN. We conclude with ~70% certainty that HESS J1943+213 does not host a pulsar. Second, long-baseline interferometry of the source with e-MERLIN at 1.5- and 5- GHz, shows only a core, a point source at ~ 1 - 100 milli-arcsecond resolution. Its 2013 flux density is about one-third lower than detected in 2011 observations with similar resolution. This radio variability of the core strengthens the HBL object hypothesis. More evidence against the PWN scenario comes, third, from the radio spectrum we compiled. The extended structure follows a power-law behavior with spectral index alpha = -0.54 +- 0.04 while the core component is flat spectrum (alpha = -0.03 +- 0.03). In contrast, the radio synchrotron emission of PWNe predicts a single power-law distribution. Overall we rule out the PWN hypothesis and conclude the source is a BL Lac object. The consistently high fraction (70%) of the flux density from the extended structure then leads us to conclude that HESS J1943+213 must be a non-classical HBL object.
We report on the 1.6 GHz (18 cm) VLBI observations of the unresolved, steady TeV source HESS J1943+213 located in the Galactic plane, performed with the European VLBI Network (EVN) in 2014. Our new observations with a nearly full EVN array provide the deepest image of HESS J1943+213 at the highest resolution ever achieved, enabling us to resolve the long-standing issues of the source identification. The milliarcsecond-scale structure of HESS J1943+213 has a clear asymmetric morphology, consisting of a compact core and a diffuse jet-like tail. This is broadly consistent with the previous e-EVN observations of the source performed in 2011, and re-analyzed in this work. The core component is characterized by the brightness temperature of $\gtrsim1.8 \times 10^9$ K, which is typical for low-luminosity blazars in general. Overall, radio properties of HESS J1943+213 are consistent with the source classification as an "extreme high-frequency-peaked BL Lac object". Remarkably, we note that since HESS J1943+213 does not reveal any optical or infrared signatures of the AGN activity, it would never be recognized and identified as a BL Lac object, if not its location close to the Galactic plane where the High Energy Stereoscopic System has surveyed, and the follow-up dedicated X-ray and radio studies triggered by the source detection in the TeV range. Our results suggest therefore a presence of an unrecognized, possibly very numerous population of particularly extreme HBLs, and simultaneously demonstrate that the low-frequency VLBI observations with high-angular resolution are indispensable for a proper identification of such objects.
Sgr B2 is a well-known star forming molecular cloud complex in the Galactic center region showing evidence of high energy activity as traced by the K$\alpha$ neutral FeI line at 6.4 keV, as well as GeV and TeV $\gamma$-ray emission. Here we present VLA and GMRT observations with respective resolutions of $\approx3.5"\times1.2"$ and 25$"\times25"$ and report the detection of an OH(1720 MHz) maser, with no accompanying OH 1665, 1667 and 1612 MHz maser emission. The maser coincides with a 150 MHz nonthermal radio source in Sgr B2(M). This rare class of OH(1720 MHz) masers or the so-called supernova remnant (SNR) masers, with no main line transitions, trace shocked gas and signal the interaction of an expanding SNR with a molecular cloud. We interpret the 150 MHz radio source as either the site of a SNR -- molecular gas interaction or a wind-wind collision in a massive binary system. The interaction of the molecular cloud and the nonthermal source enhances the cosmic-ray ionization rate, allows the diffusion of cosmic rays into the cloud and produces the variable 6.4 keV line, GeV and TeV $\gamma$-ray emission from Sgr B2(M). The cosmic ray electron interaction with the gas in the Galactic center can not only explain the measured high values of cosmic ray ionization and heating rates but also contribute to nonthermal bremsstrahlung continuum emission, all of which are consistent with observations.
(Abridged) The physical structure of deeply-embedded low-mass protostars (Class 0) on scales of less than 300 AU is still poorly constrained. Determining this is crucial for understanding the physical and chemical evolution from cores to disks. In this study two models of the emission, a Gaussian disk intensity distribution and a parametrized power-law disk model, are fitted to sub-arcsecond resolution interferometric continuum observations of five Class 0 sources, including one source with a confirmed Keplerian disk. For reference, a spherically symmetric single power-law envelope is fitted to the larger scale ($\sim$1000 AU) emission and investigated further for one of the sources on smaller scales. A thin disk model can approximate the emission and physical structure in the inner few 100 AU scales of the studied deeply-embedded low-mass protostars and paves the way for analysis of a larger sample with ALMA. While the disk radii agree with previous estimates the masses are different for some of the sources studied. Assuming a typical temperature distribution, the fractional amount of mass in the disk above 100 K varies in between 7% to 30%. Kinematic data are needed to determine the presence of any Keplerian disk. Using previous observations of p-H$_2^{18}$O, we estimate the relative gas phase water abundances roughly an order of magnitude higher than previously inferred when both warm and cold H$_2$ was used as reference. A spherically symmetric single power-law envelope model fails to simultaneously reproduce both the small and large scale emission.
We investigate the distribution of different classes of spectroscopically identified sources and theoretical models in the color-color diagrams (CCDs) combining the near-infrared (NIR) and mid-infrared (MIR) data to develop a method to classify Outer Galaxy sources detected with the Spitzer Space Telescope (hereafter Spitzer) SMOG survey in the IRAC 3.6 and 8.0 micrometer and MIPS 24 micrometer bands. We supplement the Spitzer data with the NIR data from the 2MASS and UKIDSS (JHKs) surveys, as well as with the Wide-field Infrared Survey Explorer (WISE) at 12 and 22 micrometers and AKARI (9 and 18 micrometers) MIR surveys. The main goal of our study is to discover and characterise the population of intermediate- and low-mass young stellar objects (YSOs) in the Outer Galaxy and use it to study star formation in a significantly different environment than the Galaxy inside the solar circle. Since the YSOs can be confused with evolved stars in the MIR, these classes of objects need to be carefully separated. Here we present the initial results of our analysis using the Ks-[8.0] vs. Ks-[24] CCD as an example. The evolved stars separated from YSOs in the YSO selection process will be investigated in detail in the follow-up study.
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