In recent years, multiple studies have reported substantial populations of large, low-surface-brightness galaxies in local galaxy clusters. Various theories that aim to explain the presence of such ultra-diffuse galaxies (UDGs) have since been proposed. A key question that will help to differentiate between models is whether UDGs have counterparts in lower-mass host haloes, and what their abundance as a function of halo mass is. In this study we extend our previous study of UDGs in galaxy clusters to galaxy groups. We measure the abundance of UDGs in 325 spectroscopically-selected groups from the Galaxy And Mass Assembly (GAMA) survey. We make use of the overlapping imaging from the ESO Kilo-Degree Survey (KiDS), from which we can identify galaxies with mean surface brightnesses within their effective radii down to ~25.5 mag arcsec$^{-2}$ in the r-band. We are able to measure a significant overdensity of UDGs (with sizes r_eff > 1.5 kpc) in galaxy groups down to M200=10^12 Msun, a regime where approximately only 1 in 10 groups contains a UDG that we can detect. We combine measurements of the abundance of UDGs in haloes that cover three orders of magnitude in halo mass, finding that their numbers scale quite steeply with halo mass; N_UDG (R<R200) $\propto$ M200^(1.11+/-0.07). To better interpret this, we also measure the mass-richness relation for brighter galaxies down to $M^*_r$+2.5 in the same GAMA groups, and find a much shallower relation of N_Bright (R<R200) $\propto$ M200^(0.78+/-0.05). This shows that UDGs are relatively more abundant, compared to bright galaxies, in massive clusters than in groups. We discuss implications, but whether this difference is related to a higher destruction rate of UDGs in groups, or whether massive haloes have a positive effect on their formation, is not yet clear.
We show that hard encounters in the central regions of globular clusters embedded in dark matter (DM) haloes necessarily lead to the formation of gravitationally-bound stellar envelopes that extend far beyond the nominal tidal radius of the system. Using statistical arguments and numerical techniques we derive the equilibrium distribution function of stars ejected from the centre of a non-divergent spherical potential. Independently of the velocity distribution with which stars are ejected, GC envelopes have density profiles that approach asymptotically $\rho\sim r^{-4}$ at large distances and become isothermal towards the centre. Adding a DM halo component leaves two clear-cut observational signatures: (i) a flattening, or slightly increase of the projected velocity dispersion profile at large distances, and (ii) an outer surface density profile that is systematically shallower than in models with no dark matter.
We present an optical spectrum (4000-10500 {\AA} ) of the lensed blazar B0218+357 secured at the 10m GTC and aimed to investigate and clarify the properties of this intriguing system. We found that the emission line spectrum of the blazar is characterised by only one broad emission line that interpreted as Mg II 2800 {\AA} yields z=0.95. In addition we detect narrow absorption lines of Mg II 2800 {\AA} and Ca II (H,K) and Na I 5892 {\AA} at z=0.68437 +/- 0.00005 due to intervening interstellar gas. No stellar absorption features attributable to the lens galaxy are revealed. Thus the assumed redshift of the lens is dubious. The continuum spectrum of the object exhibits a remarkable drop towards the short wavelengths likely due to a significant extinction. This extinction cannot be produced in the lens galaxy at z =0.684 with any value of R$_V$ under the assumption that the intrinsic shape of the blazar is dominated by a power law emission. However, the observed continuum is consistent with a power law emission assuming a standard (R$_V$ = 3.1) extinction at the source redshift (z=0.95) as supported also by the presence of Mg II absorptions at the same redshift. HST images of B0218+357 exhibit the double image of the source together with extended image of a face on spiral galaxy. We argue that this galaxy is possibly not the lensing galaxy but the host galaxy of the blazar. This has substantial consequences on the models of the system and on the derived values of the Hubble constant.
We investigate the stellar-mass Tully-Fisher relation (TFR) between the stellar mass and the integrated gas velocity dispersion, quantified by the kinematic estimator S_0.5 measured from strong emission lines in spectra of galaxies at 0<z<5. We combine luminosity-selected galaxies (`high-luminosity sample') with galaxies selected in other ways (`low-luminosity sample') to cover a range in stellar mass that spans almost five orders of magnitude: 7.0 < log M* < 11.5. We find that the logarithmic power-law slope and normalisation of the TFR are independent of redshift out to z~3. The scatter in the TFR is <0.5 dex such that the gas velocity dispersion can be used as a proxy for the stellar mass of a galaxy independently of its redshift. At z>3 the scatter increases and the existence of a correlation is not obvious. The high-luminosity sample exhibits a flatter slope of 1.5$\pm$0.2 at z<3 compared to the low-luminosity sample slope of 2.9$\pm$0.3, suggesting a turnover in the TFR. The combined sample is well fit with a break in the TFR at a characteristic stellar mass scale of M*~10$^{10}$ M$_{\odot}$, with no significant evolution out to z~3. We demonstrate that a break in the TFR with a steeper slope at the low-mass end is a natural consequence of galaxy models with a mass-dependent stellar to halo-mass ratio.
We use the Gaia-TGAS data to compare the transverse velocities in Galactic longitude (coming from proper motions and parallaxes) in the Milky Way disk for negative and positive longitudes as a function of distance. The transverse velocities are strongly asymmetric and deviate significantly from the expectations for an axisymmetric Galaxy. The value and sign of the asymmetry changes at spatial scales of several tens of degrees in Galactic longitude and about 0.5 kpc in distance. The asymmetry is statistically significant at 95% confidence level for 57% of the region probed, which extends up to ~1.2 kpc. A percentage of 24% of the region studied shows absolute differences at this confidence level larger than 5 km/s and 7% larger than 10 km/s. The asymmetry pattern shows mild variations in the vertical direction and with stellar type. A first qualitative comparison with spiral arm models indicates that the arms are unlikely to be the main source of the asymmetry. We briefly discuss alternative origins. This is the first time that global all-sky asymmetries are detected in the Milky Way kinematics, beyond the local neighbourhood, and with a purely astrometric sample.
We perform a post-processing radiative feedback analysis on a three-dimensional ab initio cosmological simulation of an atomic cooling halo under the direct collapse black hole (DCBH) scenario. We maintain the spatial resolution of the simulation by incorporating native ray-tracing on unstructured mesh data, including Monte Carlo Lyman-alpha (Ly{\alpha}) radiative transfer. DCBHs are born in gas-rich, metal-poor environments with the possibility of Compton-thick conditions, $N_H \gtrsim 10^{24} {\rm cm}^{-2}$. Therefore, the surrounding gas is capable of experiencing the full impact of the bottled-up radiation pressure. In particular, we find that multiple scattering of Ly{\alpha} photons provides an important source of mechanical feedback after the gas in the sub-parsec region becomes partially ionized, avoiding the bottleneck of destruction via the two-photon emission mechanism. We provide detailed discussion of the simulation environment, expansion of the ionization front, emission and escape of Ly{\alpha} radiation, and Compton scattering. A sink particle prescription allows us to extract approximate limits on the post-formation evolution of the radiative feedback. Fully-coupled Ly{\alpha} radiation hydrodynamics will be crucial to consider in future DCBH simulations.
Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Ly$\alpha$ emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts ($z\lesssim0.05$) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at $z\lesssim0.05$ (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broad band colors, and studied their properties with MMT spectroscopy. From the whole SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. (An additional 7 candidates are contaminants, and 4 remain without spectra.) These blueberries are dwarf starburst galaxies with very small sizes ($< 1\hbox{kpc}$), and very high ionization ([OIII]/[OII]$\sim10-60$). They also have some of the lowest stellar masses ($\log(\hbox{M}/\hbox{M}_{\odot})\sim6.5-7.5$) and lowest metallicities ($7.1<12+\log(\hbox{O/H})<7.8$) starburst galaxies.
We present the results of a deep Chandra observation of the X-ray bright, moderate cooling flow group NGC 5044 along with the observed correlations between the ionized, atomic, and molecular gas in this system. The Chandra observation shows that the central AGN has undergone two outbursts in the past 100 Myrs, based on the presence of two pairs of nearly bipolar X-ray cavities. The molecular gas and dust within the central 2kpc is aligned with the orientation of the inner pair of bipolar X-ray cavities, suggesting that the most recent AGN outburst had a dynamical impact on the molecular gas. NGC 5044 also hosts many X-ray filaments within the central 8kpc, but there are no obvious connections between the X-ray and H$\alpha$ filaments and the more extended X-ray cavities that were inflated during the prior AGN outburst. Using the linewidth of the blended Fe-L line complex as a diagnostic for multiphase gas, we find that the majority of the multiphase, thermally unstable gas in NGC 5044 is confined within the X-ray filaments. While the cooling time and entropy of the gas within the X-ray filaments are very similar, not all filaments show evidence of gas cooling or an association with Ha emission. We suggest that the various observed properties of the X-ray filaments are suggestive of an evolutionary sequence where thermally unstable gas begins to cool, becomes multiphased, develops Ha emitting plasma, and finally produces cold gas.
The thermal history of the Universe is included in the Debye Gravitational Theory (DGT) to describe the speed of rotation of the galaxies. The DGT incorporate the temperature of Debye in the entropic gravitational theory. According to the DGT, the expression of the rotation of the galaxies is not a continuous function of the redshift, there is a discontinuity at $\sim 0.77$. According to their redshift, the galaxies form two groups. (a) Those with redshift above 0.77 with declining rotation curves like $R^{\beta}$ with $\beta \leq -0.5$ (Newtonian regime). (b) Those with redshift below 0.77 with rising rotation curves like $R^{\beta}$ with $\beta \geq 0$ (Mondian regime). At $z\sim 0.77 $ an extra boost (Dirac delta-like twisting force) led the galaxies to spin very fast.This scenario is consistent with a mysterious entity such as the dark energy and that at $z\sim 0.77 $, in addition to accelerating the expansion, boosted the rotation of the galaxies again, inducing a transition between the Newtonian regime to the Mondian regime. It is possible to check that the characteristics on galaxy rotations provided by the DGT for a broad range of redshift from $z\sim 4$ to $z=0$ are in agreement with the observations. We believe that the change in the form of rotation of galaxies at $z\sim 0.77$ is new evidence for the hypothesis of dark energy.
Line-intensity mapping surveys probe large-scale structure through spatial variations in molecular line emission from a population of unresolved cosmological sources. Future such surveys of carbon monoxide line emission (specifically the CO(1-0) line) face potential contamination from a disjoint population of sources emitting in a hydrogen cyanide emission line, HCN(1-0). This paper explores the potential range of the strength of HCN emission and its effect on the CO auto power spectrum, using simulations with an empirical model of the CO/HCN--halo connection. We find that effects on the observed CO power spectrum vary with modeling approaches but are very small for our fiducial model, with the undesirable boost in overall CO detection significance due to HCN expected to be less than 1%.
We present the results from Atacama Large Millimeter/submillimeter Array (ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII]) and the underlying continuum of BRI 1202-0725, an interacting galaxy system at $z =$ 4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two Lyman-$\alpha$ emitters (LAEs), all within $\sim$25 kpc of the QSO. We detect the QSO and SMG in both [NII] and continuum. At the $\sim$$1"$ (or 6.6 kpc) resolution, both QSO and SMG are resolved in [NII], with the de-convolved major axes of $\sim$9 and $\sim$14 kpc, respectively. In contrast, their continuum emissions are much more compact and unresolved even at an enhanced resolution of $\sim$$0.7"$. The ratio of the [NII] flux to the existing CO (7$-$6) flux is used to constrain the dust temperature ($T_{\rm dust}$) for a more accurate determination of the FIR luminosity $L_{\rm FIR}$. Our best estimated $T_{\rm dust}$ equals $43 (\pm 2)$ K for both galaxies (assuming an emissivity index $\beta = 1.8$). The resulting $L_{\rm CO(7-6)}/L_{\rm FIR}$ ratios are statistically consistent with that of local luminous infrared galaxies, confirming that $L_{\rm CO(7-6)}$ traces the star formation (SF) rate (SFR) in these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of 5.1 $(6.9) \times 10^3 M_{\odot}$ yr$^{-1}$ ($\pm$ 30%) assuming Chabrier initial mass function, takes place within a diameter (at half maximum) of 1.3 (1.5) kpc, and shall consume the existing 5 $(5) \times 10^{11} M_{\odot}$ of molecular gas in 10 $(7) \times 10^7$ years.
The nearby galaxies of the Local Group can act as our laboratories in helping to bridge the gap between theory and observations. In this review we will describe the complications of identifying samples of OB stars, yellow and red supergiants, and Wolf-Rayet stars, and what we have so far learned from these studies.
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We present a BVI optical photometric study of the old open cluster Ruprecht 6 using the data obtained with the SMARTS 1.0 m telescope at the CTIO, Chile. Its color-magnitude diagrams show the clear existence of the main-sequence stars, of which turn-off point is located around V ~ 18.45 mag and B-V ~ 0.85 mag. Three red clump (RC) stars are identified at V = 16.00 mag, I = 14.41 mag and B-V = 1.35 mag. From the mean Ks-band magnitude of RC stars (Ks=12.39 +- 0.21 mag) in Ruprecht 6 from 2MASS photometry and the known absolute magnitudes of the RC stars (M_Ks = -1.595 +- 0.025 mag), we obtain the distance modulus to Ruprecht 6 (m-M)_0 = 13.84 +- 0.21 mag (d=5.86 +- 0.60 kpc). From the (J-K_s) and (B-V) colors of the RC stars, comparison of the (B-V) and (V-I) colors of the bright stars in Ruprecht 6 with those of the intrinsic colors of dwarf and giant stars, and the PARSEC isochrone fittings, we derive the reddening values of E(B-V) = 0.42 mag and E(V-I) = 0.60 mag. Using the PARSEC isochrone fittings onto the color-magnitude diagrams, we estimate the age and metallicity to be: log (t) =9.50 +- 0.10 (t =3.16 +- 0.82 Gyr) and [Fe/H] = -0.42 +- 0.04 dex. We present the Galactocentric radial metallicity gradient analysis for old (age > 1 Gyr) open clusters of Dias et al. catalog, which likely follow a single relation of [Fe/H] =(-0.034 +- 0.007) R_GC + (0.190 +- 0.080) (rms = 0.201) for the whole radial range or dual relation of [Fe/H] =(-0.077 +- 0.017) R_GC + (0.609 +- 0.161) (rms = 0.152) and constant ([Fe/H] ~ -0.3 dex) value, inside and outside of R_GC ~ 12 kpc, respectively. The metallicity and Galactocentric radius (13.28 +- 0.54 kpc) of Ruprecht 6 obtained in this study seem to be consistent with both of the relations.
Pre-stellar cores represent the initial conditions in the process of star and
planet formation, therefore it is important to study their physical and
chemical structure. Because of their volatility, nitrogen-bearing molecules are
key to study the dense and cold gas present in pre-stellar cores. The NH_3
rotational transition detected with Herschel-HIFI provides a unique combination
of sensitivity and spectral resolution to further investigate physical and
chemical processes in pre-stellar cores. Here we present the velocity-resolved
Herschel-HIFI observations of the ortho-NH_3(1_0-0_0) line at 572 GHz and study
the abundance profile of ammonia across the pre-stellar core L1544 to test
current theories of its physical and chemical structure.
Recently calculated collisional coefficients have been included in our
non-LTE radiative transfer code to reproduce Herschel observations. A gas-grain
chemical model, including spin-state chemistry and applied to the (static)
physical structure of L1544 is also used to infer the abundance profile of
ortho-NH_3 . The hyperfine structure of ortho-NH_3(1_0-0_0) is resolved for the
first time in space. All the hyperfine components are strongly self-absorbed.
The profile can be reproduced if the core is contracting in quasi-equilibrium,
consistent with previous work, and if the NH_3 abundance is slightly rising
toward the core centre, as deduced from previous interferometric observations
of para-NH_3(1,1). The chemical model overestimates the NH_3 abundance at radii
between ~ 4000 and 15000 AU by about two orders of magnitude and underestimates
the abundance toward the core centre by more than one order of magnitude. Our
observations show that chemical models applied to static clouds have problems
in reproducing NH_3 observations.
We estimate the dust torus cooling timescale once the active galactic nucleus (AGN) is quenched. In a clumpy torus system, once the incoming photons are suppressed, the cooling timescale of one clump from $T_{\rm dust}=1000$ K to several $10$ K is less than $10$ years, indicating that the dust torus cooling time is mainly governed by the light crossing time of the torus from the central engine. After considering the light crossing time of the torus, the AGN torus emission at $12~\mu$m becomes over two orders of magnitude fainter within $100$ years after the quenching. We also propose that those "dying" AGN could be found using the AGN indicators with different physical scale $R$ such as $12~\mu$m band luminosity tracing AGN torus ($R \sim 10$ pc) and the optical [OIII]$\lambda5007$ emission line narrow line regions ($R=10^{2-4}$ pc).
We present nebular emission associated with 198 strong Mg II absorbers at 0.35 $\le z \le$ 1.1 in the fibre spectra of quasars from the Sloan Digital Sky Survey. Measured [O II] luminosities (L$_{[O II]}$) are typical of sub-L$^{\star}$ galaxies with derived star formation rate (uncorrected for fibre losses and dust reddening) in the range of 0.5-20 ${\rm M_\odot\ yr^{-1}}$. Typically less than $\sim$ 3% of the Mg II systems with rest equivalent width, $W_{2796}$ $\ge$ 2 \AA, show L$_{[O II]} \ge 0.3$ L$^{\star}_{[O II]}$. The detection rate is found to increase with increasing $W_{2796}$ and $z$. No significant correlation is found between $W_{2796}$ and L$_{[O II]}$ even when we restrict the samples to narrow $z$-ranges. A strong correlation is seen between L$_{[O II]}$ and $z$. While this is expected from the luminosity evolution of galaxies, we show finite fibre size plays a very crucial role in this correlation. The measured nebular line ratios (like [O III]/[O II] and [O III]/H$\beta$) and their $z$ evolution are consistent with those of galaxies detected in deep surveys. Based on the median stacked spectra, we infer the average metallicity (log Z $\sim$8.3), ionization parameter (log $q$ $\sim$7.5) and stellar mass (log (M/M$_\odot$)$\sim$9.3). The Mg II systems with nebular emission typically have $W_{2796}$ $\ge 2$ \AA, Mg II doublet ratio close to 1 and W(Fe II$\lambda$2600)/$W_{2796}$ $\sim 0.5$ as often seen in damped Ly$\alpha$ and 21-cm absorbers at these redshifts. This is the biggest reported sample of [O II] emission from Mg II absorbers at low impact parameters ideally suited for probing various feedback processes at play in $z\le 1$ galaxies.
There is a large degree of variety in the optical variability of quasars and it is unclear whether this is all attributable to a single (set of) physical mechanism(s). We present the results of a systematic search for major flares in AGN in the Catalina Real-time Transient Survey as part of a broader study into extreme quasar variability. Such flares are defined in a quantitative manner as being atop of the normal, stochastic variability of quasars. We have identified 51 events from over 900,000 known quasars and high probability quasar candidates, typically lasting 900 days and with a median peak amplitude of $\Delta m = 1.25$ mag. Characterizing the flare profile with a Weibull distribution, we find that nine of the sources are well described by a single-point single-lens model. This supports the proposal by Lawrence et al. (2016) that microlensing is a plausible physical mechanism for extreme variability. However, we attribute the majority of our events to explosive stellar-related activity in the accretion disk: superluminous supernovae, tidal disruption events, and mergers of stellar mass black holes.
We present new [Ne II] (12.8 micron) IRTF/TEXES observations of the Galactic Center HII regions H1 and H2, which are at a projected distance of ~11 pc from the center of the Galaxy. The new observations allow to map the radial velocity distributions of ionized gas. The high spectroscopic resolution (~4 km/s) helps us to disentangle different velocity components and enables us to resolve previous ambiguity regarding the nature of these sources. The spatial distributions of the intensity and radial velocity of the [Ne II] line are mapped. In H1, the intensity distributions of the Paschen-\alpha (1.87 micron) and [Ne II] lines are significantly different, which suggests a strong variation of extinction across the HII region of A_K~0.56. The radial velocity distributions across these HII regions are consistent with the predictions of a bow-shock model for H1 and the pressure-driven model for H2. Furthermore, we find a concentration of bright stars in H2. These stars have similar H-K_s colors and can be explained as part of a 2 Myr old stellar cluster. H2 also falls on the orbit of the molecular clouds, suggested to be around Sgr A*. Our new results confirm what we had previously suggested: the O supergiant P114 in H1 is a runaway star, moving towards us through the -30-0 {km/s} molecular cloud, whereas the O If star P35 in H2 formed in-situ, and may mark the position of a so-far unknown small star cluster formed within the central 30 pc of the Galaxy.
We study the effect of the instantaneous gas expulsion on star clusters wherein the residual gas has a density profile shallower than that of the embedded cluster. This is expected if star formation proceeds with a given SFE per free-fall time in a centrally-concentrated molecular clump. We perform direct N-body simulations whose initial conditions are generated by the program "mkhalo" "falcON" adapted for our models. Our model clusters initially have a Plummer profile and are in virial equilibrium with the gravitational potential of the cluster-forming clump. The residual gas contribution is computed based on the model of Parmentier&Pfalzner(2013). Our simulations include mass loss by stellar evolution and the tidal field of the Galaxy. We find that a star cluster with a minimum global SFE of 15% is able to survive instantaneous gas expulsion and to produce a bound cluster. Its violent relaxation lasts no longer than 20 Myr, independently of its global SFE and initial stellar mass. At the end of violent relaxation the bound fractions of surviving clusters with the same global SFEs are similar regardless of their initial stellar mass. Their subsequent lifetime in the gravitational field of the Galaxy depends on their bound stellar masses. We therefore conclude that the critical SFE needed to produce a bound cluster is 15%, which is twice smaller than earlier estimates of 33%. Thus we have improved the survival likelihood of young clusters after instantaneous gas expulsion. Those can now survive instantaneous gas expulsion with global SFEs as low as those observed for embedded clusters of Solar Neighbourhood (15-30%). This is the consequence of the star cluster having a density profile steeper than that of the residual gas. However, in terms of the effective SFE, measured by the virial ratio of the cluster at gas expulsion, our results are in agreement with previous studies.
We used four-year baseline HST/WFC3 IR observations of the Galactic Centre in the F153M band (1.53 micron) to identify variable stars in the central ~2.3'x2.3' field. We classified 3845 long-term (periods from months to years) and 76 short-term (periods of a few days or less) variables among a total sample of 33070 stars. For 36 of the latter ones, we also derived their periods (<3 days). Our catalog not only confirms bright long period variables and massive eclipsing binaries identified in previous works, but also contains many newly recognized dim variable stars. For example, we found \delta Scuti and RR Lyrae stars towards the Galactic Centre for the first time, as well as one BL Her star (period < 1.3 d). We cross-correlated our catalog with previous spectroscopic studies and found that 319 variables have well-defined stellar types, such as Wolf-Rayet, OB main sequence, supergiants and asymptotic giant branch stars. We used colours and magnitudes to infer the probable variable types for those stars without accurately measured periods or spectroscopic information. We conclude that the majority of unclassified variables could potentially be eclipsing/ellipsoidal binaries and Type II Cepheids. Our source catalog will be valuable for future studies aimed at constraining the distance, star formation history and massive binary fraction of the Milky Way nuclear star cluster.
This review describes our current understanding of interstellar extinction. This differ substantially from the ideas of the 20th century. With infrared surveys of hundreds of millions of stars over the entire sky, such as 2MASS, SPITZER-IRAC, and WISE, we have looked at the densest and most rarefied regions of the interstellar medium at distances of a few kpc from the sun. Observations at infrared and microwave wavelengths, where the bulk of the interstellar dust absorbs and radiates, have brought us closer to an understanding of the distribution of the dust particles on scales of the Galaxy and the Universe. We are in the midst of a scientific revolution in our understanding of the interstellar medium and dust. Progress in, and the key results of, this revolution are still difficult to predict. Nevertheless, (a) a physically justified model has been developed for the spatial distribution of absorbing material over the nearest few kiloparsecs, including the Gould belt as a dust container, which gives an accurate estimate of the extinction for any object just in terms of its galactic coordinates. It is also clear that (b) the interstellar medium makes up roughly half the mass of matter in the galactic vicinity of the solar system (the other half is made up of stars, their remnants, and dark matter) and (c) the interstellar medium and, especially, dust, differ substantially in different regions of space, and deep space cannot be understood by only studying nearby space.
Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K>15) stellar population in the Milky Way's nuclear cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the dim oldest stellar population. Recently, we analyzed HST WFC3/IR observations of the central 2.3 arcminx2.3 arcmin (~5x5 pc^2) of the Milky Way and found 21 variable stars with 0.2 d<P<1 d. Here, we present a further comprehensive analysis of these stars. The period-luminosity relationship of RR Lyrae stars was used to derive their foreground extinctions and distances. Using multiple approaches, we classified our sample as four RRc, four and three candidate RRab and ten binaries. Especially, the four RRabs show sawtooth light curves and fall exactly onto the Oosterhoff I division in the Bailey diagram. Compared to the RRabs reported by Minniti et al, 2016, our four new RRabs have higher extinction (A_K>1.8) and should be closer to the Galactic Nuclear Bulge. The extinction and distance of one RRab match those for the nuclear star cluster given in the previous works. We perform simulations and find that after correcting for incompleteness, there could be no more than 40 RRabs within the nuclear star cluster and in our field-of-view. Through comparing with the number of RRabs in the known globular clusters in the Milky Way, we estimate that if there exists an old, metal-poor (-1.5<[Fe/H]<-1) stellar population in the Milky Way nuclear star cluster, then it contributes at most 4.4x10^5 M, i.e. ~17% of the stellar mass.
Simulations are expected to be the powerful tool to investigate the baryon effects on dark matter (DM) halos. Recent high resolution, cosmological hydrodynamic simulations (\citealt{Cintio14}, DC14) predict that the inner density profiles of DM halos depend systematically on the ratio of stellar to DM mass ($M_{\ast}/M_{\rm halo}$) which is thought to be able to provide good fits to the observed rotation curves of galaxies. The DC14 profile is fitted from the simulations which are confined to $M_{\rm halo}\le 10^{12}M_{\sun}$, in order to investigate the physical processes that may affect all halos, we extrapolate it to much larger halo mass, including that of galaxy clusters. The inner slope of DC14 profile is flat for low halo mass, it approaches 1 when the halo mass increases towards $10^{12}M_{\sun}$ and decreases rapidly after that mass. We use DC14 profile for lenses and find that it predicts too few lenses compared with the most recent strong lensing observations SQLS (\citealt{Inada12}). We also calculate the strong lensing probabilities for a simulated density profile which continues the halo mass from the mass end of DC14 ($\sim 10^{12}M_{\sun}$) to the mass that covers the galaxy clusters (\citealt{Schaller15}, Schaller15), and find that this Schaller15 model predict too many lenses compared with other models and SQLS observations. Interestingly, Schaller15 profile has no core, however, like DC14, the rotation curves of the simulated halos are in excellent agreement with observational data. Furthermore, we show that the standard two-population model SIS+NFW cannot match the most recent SQLS observations for large image separations.
Observations with the Chandra X-ray Observatory are used to examine the hot gas properties within a sample of 10 galaxy groups selected from the Galaxy And Mass Assembly survey's optical Friends-of-Friends group catalogue. Our groups have been screened to eliminate spurious and unrelaxed systems, and the effectiveness of this procedure is demonstrated by the detection of intergalactic hot gas in 80 per cent of our sample. However, we find that 9 of the 10 are X-ray underluminous by a mean factor of $\sim$4 compared to typical X-ray-selected samples. Consistent with this, the majority of our groups have gas fractions that are lower and gas entropies somewhat higher than those seen in typical X-ray-selected samples. Two groups, which have high 2{\sigma} lower limits on their gas entropy, are candidates for the population of high-entropy groups predicted by some active galactic nucleus feedback models.
We present a new analysis of the stellar mass function and morphology of recently-quenched galaxies (RQGs), whose star formation has been recently quenched for some reason. The COSMOS2015 catalog was exploited to select those galaxies at 0.2 < z < 4.8, over 1.5 deg2 of the Cosmic Evolution Survey (COSMOS) UltraVISTA field. This is the first time that RQGs are consistently selected and studied in such a wide range of redshift. We find increasing number density of RQGs with time in a broad mass range at z>1, while low-mass RQGs start to grow very rapidly at z < 1. We also demonstrate that the migration of RQGs may largely drive the evolution of the stellar mass function of passive galaxies. Moreover, we find that the morphological type distribution of RQGs are intermediate between those of star-forming and passive galaxies. These results indicate that RQGs represent a major transitional phase of galaxy evolution, in which star-forming galaxies turn into passive galaxies, accompanied by the build up of spheroidal component.
The interaction of a hot, high-velocity wind with a cold, dense molecular cloud has often been assumed to resemble the evolution of a cloud embedded in a post-shock flow. However, no direct comparative study of these two processes currently exists in the literature. We present 2D adiabatic hydrodynamical simulations of the interaction of a Mach 10 shock with a cloud of density contrast $\chi = 10$ and compare our results with those of a commensurate wind-cloud simulation. We then investigate the effect of varying the wind velocity, effectively altering the wind Mach number $M_{wind}$, on the cloud's evolution. We find that there are significant differences between the two processes: 1) the transmitted shock is much flatter in the shock-cloud interaction; 2) a low-pressure region in the wind-cloud case deflects the flow around the edge of the cloud in a different manner to the shock-cloud case; 3) there is far more axial compression of the cloud in the case of the shock. As $M_{wind}$ increases, the normalised rate of mixing is reduced. Clouds in winds with higher $M_{wind}$ also do not experience a transmitted shock through the cloud's rear and are more compressed axially. In contrast with shock-cloud simulations, the cloud mixing time normalised by the cloud-crushing time-scale $t_{cc}$ increases for increasing $M_{wind}$ until it plateaus (at $t_{mix} \simeq 25 \, t_{cc}$) at high $M_{wind}$, thus demonstrating the expected Mach scaling. In addition, clouds in high Mach number winds are able to survive for long durations and are capable of being moved considerable distances.
Narrowband imaging is a highly successful approach for finding large numbers of high redshift Ly$\alpha$ emitting galaxies (LAEs) up to $z\sim6.6$. However, at $z\gtrsim 7$ there are as yet only 3 narrowband selected LAEs with spectroscopic confirmations (two at z $\sim$ 6.9-7.0, one at z $\sim$ 7.3), which hinders extensive studies on cosmic re-ionization and galaxy evolution at this key epoch. We have selected 23 candidate z $\approx$ 6.9 LAEs in COSMOS field with the large area narrowband survey LAGER (Lyman-Alpha Galaxies at the End of Reionization). In this work we present spectroscopic followup observations of 12 candidates using IMACS on Magellan. For 9 of these, the observations are sufficiently deep to detect the expected lines. Ly$\alpha$ emission lines are identified in six sources (yielding a success rate of 2/3), including 3 luminous LAEs with Ly$\alpha$ luminosities of L$_{Ly\alpha}$ $\sim$ 10$^{43.4}$ erg s$^{-1}$. This triples the sample size of spectroscopically confirmed narrowband selected LAEs at $z\gtrsim 7$, and confirms the bright end bump in the Ly$\alpha$ luminosity function we previously derived based on the photometric sample, supporting a patchy re-ionization scenario. Two luminous LAEs appear physically linked with projected distance of 1.1 pMpc and velocity difference of $\sim$ 170 km/s. They likely sit in a common ionized bubble produced by themselves or with close neighbors, which reduces the IGM attention to Ly$\alpha$. A tentative narrow N$_V$ $\lambda$1240 line is seen in one of the source, hinting activity of the central massive black hole with metal rich line emitting gas.
Open Clusters have long been used to study the chemo-dynamical evolution of the Galactic disk. This requires an homogeneously analysed sample covering a wide range of ages and distances. In this aper we present the OCCASO second data release. This comprises a sample of high-resolution ($R>65,000$) and high signal-to-noise spectra of 115 Red Clump stars in 18 Open Clusters. We derive atmospheric parameters ($T_{\mathrm{eff}}$, $\log g$, $\xi$), and [Fe/H] abundances using two analysis techniques: equivalent widths and spectral synthesis. A detailed comparison and a critical review of the results of the two methods are made. Both methods are carefully tested between them, with the \emph{Gaia} FGK Benchmark stars, and with an extensive sample of literature values. We perform a membership study using radial velocities and the resulting abundances. Finally, we compare our results with a chemo-dynamical model of the Milky Way thin disk concluding that the oldest Open Clusters are consistent with the models only when dynamical effects are taken into account.
Using a cosmological $N$-body simulation, we investigate the origin and distribution of stars in the intracluster light (ICL) of a Fornax-like cluster. In a dark matter only simulation we identify a halo which, at $z=0$, has $M_200 \simeq 4.1 \times 10^{13}M_{sun}$ and $r_{200} = 700kpc$, and replace infalling subhalos with models that include spheroid and disc components. As they fall into the cluster, the stars in some of these galaxies are stripped from their hosts, and form the ICL. We consider the separate contributions to the ICL from stars which originate in the haloes and the discs of the galaxies. We find that disc ICL stars are more centrally concentrated than halo ICL stars. The majority of the disc ICL stars are associated with one initially disc-dominated galaxy that falls to the centre of the cluster and is heavily disrupted, producing part of the cD galaxy. At radial distances greater than 200kpc, well beyond the stellar envelope of the cD galaxy, stars formerly from the stellar haloes of galaxies dominate the ICL. Therefore at large distances, the ICL population is dominated by older stars.
To probe the star formation (SF) process, we present a multi-wavelength study of IRAS 05480+2545 (hereafter I05480+2545). Analysis of Herschel data reveals a massive clump (M_clump ~ 1875 Msun; peak N(H_2) ~ 4.8 x 10^{22} cm^{-2}; A_V ~ 51 mag) containing the 6.7 GHz methanol maser and I05480+2545, which is also depicted in a temperature range of 18-26 K. Several noticeable parsec-scale filaments are detected in the Herschel 250 microns image and seem to be radially directed to the massive clump. It resembles more of a "hub-filament" system. Deeply embedded young stellar objects (YSOs) have been identified using the 1-5 microns photometric data, and a significant fraction of YSOs and their clustering are spatially found toward the massive clump, revealing the intense SF activities. An infrared counterpart (IRc) of the maser is investigated in the Spitzer 3.6-4.5 microns images. The IRc does not appear point-like source and is most likely associated with the molecular outflow. Based on the 1.4 GHz and Halpha continuum images, the ionized emission is absent toward the IRc, indicating that the massive clump harbors an early phase of massive protostar before the onset of an ultracompact H II region. Together, the I05480+2545 is embedded in a very similar "hub-filament" system to those seen in Rosette Molecular Cloud. The outcome of the present work indicates the role of filaments in the formation of the massive star-forming clump and cluster of YSOs, which might help channel material to the central hub configuration and the clump/core.
The metallicity gradients of the stellar populations in disc galaxies and their evolution store relevant information on the disc formation history and on those processes which could mix stars a posteriori, such as migration, bars and/or galaxy-galaxy interactions. We aim to investigate the evolution of the metallicity gradients of the whole stellar populations in disc components of simulated galaxies in a cosmological context. We analyse simulated disc galaxies selected from a cosmological hydrodynamical simulation that includes chemical evolution and a physically motivated Supernova feedback capable of driving mass-loaded galactic winds. We detect a mild evolution with redshift in the metallicity slopes of $-0.02 \pm 0.01$ dex~kpc$^{-1}$ from $z\sim 1$. If the metallicity profiles are normalised by the effective radius of the stellar disc, the slopes show no clear evolution for $z < 1$, with a median value of approximately $-0.23$ dex ~$r_{\rm reff}^{-1}$. As a function of stellar mass, we find that metallicity gradients steepen for stellar masses smaller than $\sim 10^{10.3} {\rm M_{\odot}}$ while the trend reverses for higher stellar masses, in the redshift range $z=[0,1]$. Galaxies with small stellar masses have discs with larger $r_{\rm reff}$ and flatter metallicity gradients than expected. We detect migration albeit weaker than in previous works. Our stellar discs show a mild evolution of the stellar metallicity slopes up to $z\sim 1,$ which is well-matched by the evolution calculated archeologically from the abundance distributions of mono-age stellar populations at $z\sim 0$. Overall, Supernova feedback could explain the trends but an impact of migration can not be totally discarded. Galaxy-galaxy interactions or small satellite accretions can also contribute to modify the metallicity profiles in the outer parts. [abridged]
We present a series of adaptive mesh refinement (AMR) hydrodynamic simulations of flat rotation curve galactic gas disks with a detailed treatment of the interstellar medium (ISM) physics of the atomic to molecular phase transition under the influence of diffuse FUV radiation fields and cosmic ray backgrounds. We explore the effects of different FUV intensities, including a model with a radial gradient designed to mimic the Milky Way. The effects of cosmic rays, including radial gradients in their heating and ionization rates, are also explored. The final simulations in this series achieve $4\:$pc resolution across the $\sim20\:$kpc global disk diameter, with heating and cooling followed down to temperatures of $\sim10\:$K. The disks are evolved for $300\:$Myr, which is enough time for the ISM to achieve a quasi-statistical equilibrium. In particular, the mass fraction of molecular gas stabilizes by $\sim$200 Myr. Additional global ISM properties are analysed. Giant molecular clouds (GMCs) are also identified and the statistical properties of their populations examined. GMCs are tracked as the disks evolve. GMC collisions, which may be a means of triggering star cluster formation, are counted and the rates compared with analytic models. Relatively frequent GMC collision rates are seen in these simulations and their implications for understanding GMC properties, including the driving of internal turbulence, are discussed.
We present BVRI photometry of supernova (SN) 2016coj in NGC 4125 from $9$ days before to $57$ days after its $B$-band maximum light. Our light curves and color curves suggest that this event belongs to the "normal" class of type Ia SNe, with a decline rate parameter $\Delta m_{15}(B) = 1.32 \pm 0.10$, and that it suffers little extinction. Adopting a distance modulus to its host galaxy of $(m - M) = 31.89$ mag, we compute extinction-corrected peak absolute magnitudes of $M_B = -19.01$, $M_V = -19.05$, $M_R = -19.03$, and $M_I = -18.79$. The explosion occurred close enough to the nucleus of NGC 4125 to hinder the measurement of its brightness. We describe our methods to reduce the effect of such host-galaxy contamination, but it is clear that our latest values suffer from systematic bias.
The mass of a protoplanetary disk limits the formation and future growth of any planet. Masses of protoplanetary disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. To investigate the utility of CO as an alternate probe of disk mass, we use ALMA to survey $^{13}$CO and C$^{18}$O J = $3-2$ line emission from a sample of 93 protoplanetary disks around stars and brown dwarfs with masses from 0.03 -- 2 M$_{\odot}$ in the nearby Chamaeleon I star-forming region. We detect $^{13}$CO emission from 17 sources and C$^{18}$O from only one source. Gas masses for disks are then estimated by comparing the CO line luminosities to results from published disk models that include CO freeze-out and isotope-selective photodissociation. Under the assumption of a typical ISM CO-to-H$_2$ ratios of $10^{-4}$, the resulting gas masses are implausibly low, with an average gas mass of $\sim$ 0.05 M$_{Jup}$ as inferred from the average flux of stacked $^{13}$CO lines. The low gas masses and gas-to-dust ratios for Cha I disks are both consistent with similar results from disks in the Lupus star-forming region. The faint CO line emission may instead be explained if disks have much higher gas masses, but freeze-out of CO or complex C-bearing molecules is underestimated in disk models. The conversion of CO flux to CO gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. CO emission lines will only be a good tracer of the disk mass when models for C and CO depletion are confirmed to be accurate.
An improved version of the 3D stellar reddening map in a space with a radius of 1200 pc around the Sun and within 600 pc of the Galactic midplane is presented. As in the previous 2010 and 2012 versions of the map, photometry with an accuracy better than $0.05^m$ in the $J$ and $K_s$ bands for more than 70 million stars from the 2MASS catalogue is used in the new version. However, the data reduction technique is considerably more complicated. As before, an analysis of the distribution of stars near the main-sequence turnoff on the $(J-K_s)$ - $K_s$ diagram, where they form a distribution maximum, provides a basis for the method. The shift of this maximum, i.e., the $mode(J-K_s)$, along $(J-K_s)$ and $K_s$, given the spatial variations of the mean de-reddened color $(J-K_s)_0$ of these stars, is interpreted as a growth of the reddening with increasing distance. The main distinction of the new method is that instead of the fixed mean absolute magnitude, de-reddened color, distance, and reddening for each cell, the individual values of these quantities are calculated for each star by iterations when solving the system of equations relating them. This has allowed one to increase the random accuracy of the map to $0.01^m$ and its spatial resolution to 20 pc in coordinates and distance and to $1^{\circ}$ in longitude and latitude. Comparison with other reddening estimates for the same spatial cells and Gaia DR1 TGAS stars shows that the constructed map is one of the best maps for the space under consideration. Its systematic errors have been estimated to be $\sigma(E(J-K_s))=0.025^m$, or $\sigma(E(B-V))=0.04^m$. The main purpose of the map is to analyze the characteristics of Galactic structures, clouds, and cloud complexes. For this purpose, the reddening map within each spatial cell has also been computed by analyzing the reddening along each line of sight.
The stellar composition of the Tycho-2 Catalogue in the range $0.75<B-V<1.25$ has been reproduced through Monte Carlo simulations. For young and old stars of the red giant clump (RGC), the red giant branch, subgiants, red dwarfs, and thick-disk giants, we have specified the distributions in coordinates, velocities, $B-V$, and $M_V$ as a function of $B-V$ and calculated their reduced proper motions, photometric distances from the $(B-V)-M_V$ calibration, and photoastrometric distances from the reduced proper motion -- $M_V$ calibration. Our simulations have shown the following: (1) a sample of thin-disk giants within 500 pc with an admixture of less than 10\% of other stars can be produced; (2) a sample of dwarfs within 100 pc almost without any admixture of other stars can be produced; (3) the Local Spiral Arm affects the RGC composition of any magnitude-limited catalog in favor of giants younger than 2 Gyr; (4) the samples produced using reduced proper motions can be used for kinematic studies, provided that the biases of the quantities being determined are simulated and taken into account; (5) the photometric distances correlate with the photoastrometric ones because of the correlation between the proper motion and magnitude; (6) the photometric distances are closer to the true ones for the red giant branch and red dwarfs as the categories of stars with a clear $(B-V)-M_V$ relation, while the photoastrometric distances are closer to the true ones for the RGC, subgiants, and thick-disk giants; (7) the calculated distances differ systematically from the true ones, but they can be used to analyze the three-dimensional distribution of stars. Our simulations confirm the validity of our previous selection of RGC stars from Tycho-2.
Making a simple model of gravitational collapse in cosmology and astrophysics, this paper examines the creation and destruction of kinetic theory entropy after a small perturbation is introduced into a homogeneous distribution of self-gravitating particles. To keep the problem tractable, gravity is Newtonian and the focus is on a coarse-grained slice of entropy constructed from the one- and two-particle distribution functions. The slice chosen is asymptotically-dominant, in the sense that it will eventually dominate over all other entropy associated with a given scale within the system. Its entropy is destroyed within a central sphere near the initial location of the perturbation - the core - and created in a surrounding shell - the halo. The core-halo transition radii are not fixed, but are proportional to the coarse-graining length used. At leading order, creation and destruction are in balance. At next-to-leading order, destruction predominates, the rate of destruction being proportional to an exponent of the time elapsed after the perturbation was introduced, and further proportional to the square of the perturbation size, divided by the square of the coarse-graining volume. For late times, destruction of asymptotic coarse-grained entropy is at least offset by entropy creation ever further from the central perturbation. We can interpret this as gravitational collapse leading to local large-scale structure formation - that is, destruction of coarse-grained entropy - at least offset by ever more distant creation of disorder. Making a plausible assumption about the application of the second law of thermodynamics to coarse-grained entropy, that distant disorder would itself be large scale.
We present Submillimeter Array (SMA) observations at 345 GHz towards the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern towards the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km/s, converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with MHD simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (~0.1 pc) of NGC 6334 V towards the higher-density hot core region (~0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.
We present the results of a multi-wavelength investigation of the very X-ray
luminous galaxy cluster MACSJ0553.4$-$3342 ($z{=}0.4270$; hereafter MACSJ0553).
Combining high-resolution data obtained with the Hubble Space Telescope and the
Chandra X-ray Observatory with groundbased galaxy spectroscopy, our analysis
establishes the system unambiguously as a binary, post-collision merger of
massive clusters. Key characteristics include perfect alignment of luminous and
dark matter for one component, a separation of almost 650 kpc (in projection)
between the dark-matter peak of the other subcluster and the second X-ray peak,
extremely hot gas (k$T{>}15$ keV) at either end of the merger axis, a potential
cold front in the East, an unusually low gas mass fraction of approximately
0.075 for the western component, a velocity dispersion of $1490_{-130}^{+104}$
km s$^{-1}$, and no indication of significant substructure along the line of
sight.
We propose that the MACSJ0553 merger proceeds not in the plane of the sky,
but at a large inclination angle, is observed very close to turnaround, and
that the eastern X-ray peak is the cool core of the slightly less massive
western component that was fully stripped and captured by the eastern
subcluster during the collision. If correct, this hypothesis would make
MACSJ0553 a superb target for a competitive study of ram-pressure stripping and
the collisional behavior of luminous and dark matter during cluster formation.
We present ALMA observations of the 2M1207 system, a young binary made of a brown dwarf with a planetary-mass companion at a projected separation of about 40 au. We detect emission from dust continuum at 0.89 mm and from the $J = 3 - 2$ rotational transition of CO from a very compact disk around the young brown dwarf. The small radius found for this brown dwarf disk may be due to truncation from the tidal interaction with the planetary-mass companion. Under the assumption of optically thin dust emission, we estimated a dust mass of 0.1 $M_{\oplus}$ for the 2M1207A disk, and a 3$\sigma$ upper limit of $\sim 1~M_{\rm{Moon}}$ for dust surrounding 2M1207b, which is the tightest upper limit obtained so far for the mass of dust particles surrounding a young planetary-mass companion. We discuss the impact of this and other non-detections of young planetary-mass companions for models of planet formation, which predict the presence of circum-planetary material surrounding these objects.
Wave dark matter ($\psi \rm{DM}$) composed of extremely light bosons ($m_{\psi} \sim 10^{-22}\,\rm eV$), with quantum pressure suppressing structures below a kpc-scale de Broglie wavelength, has become a viable dark matter candidate. Compared to the conventional free-particle $\psi {\rm DM}$ (${\rm FP} \psi {\rm DM}$), the extreme-axion $\psi \rm{DM}$ model (${\rm EA} \psi {\rm DM}$) proposed by Zhang & Chiueh (2017) features a larger cut-off wavenumber and a broad spectral bump in the matter transfer function. Here we conduct cosmological simulations to compare the halo abundances and assembly histories at $z=4-11$ between three different scenarios: ${\rm FP} \psi {\rm DM}$, ${\rm EA} \psi {\rm DM}$, and cold dark matter (CDM). We show that ${\rm EA} \psi {\rm DM}$ produces significantly more abundant low-mass haloes than ${\rm FP} \psi {\rm DM}$ with the same $m_{\psi}$, and therefore could alleviate the tension in $m_{\psi}$ required by the Ly$\alpha$ forest data and by the kpc-scale dwarf galaxy cores. We also find that, compared to the CDM counterparts, massive ${\rm EA} \psi {\rm DM}$ haloes are on average $3-4$ times more massive at $z=10-11$ due to their earlier formation, undergo a slower mass accretion at $7 \lesssim z \lesssim 11$, and then show a rapidly rising major merger rate exceeding CDM by $\sim 50\%$ at $4 \lesssim z \lesssim 7$. This fact suggests that ${\rm EA} \psi {\rm DM}$ haloes may exhibit more prominent starbursts at $z \lesssim 7$.
The relation between the mass and integrated electron pressure of galaxy group and cluster halos can be probed by stacking maps of the thermal Sunyaev-Zel'dovich (tSZ) effect. Perhaps surprisingly, recent observational results have indicated that the scaling relation between integrated pressure and mass follows the prediction of simple, self-similar models down to halo masses as low as $10^{12.5} M_{\odot}$. Hydrodynamical simulations that incorporate energetic feedback processes suggest that gas should be depleted from such low-mass halos, thus decreasing their tSZ signal relative to self-similar predictions. Here, we build on the modeling of Vikram, Lidz, and Jain (2017) to evaluate the bias in the interpretation of stacked tSZ measurements due to the signal from correlated halos (the "two-halo" term), which has generally been neglected in the literature. We fit theoretical models to a measurement of the tSZ -- galaxy group cross-correlation function, accounting explicitly for the one- and two- halo contributions. We find moderate evidence of a deviation from self-similarity in the pressure -- mass relation, even after marginalizing over conservative miscentering effects. We explore pressure -- mass models with a break at $10^{14} M_{\odot}$, as well as other variants. We discuss and test for sources of uncertainty in our analysis, in particular a possible bias in the halo mass estimates and the coarse resolution of the Planck beam. We compare our findings with earlier analyses by exploring the extent to which halo isolation criteria can reduce the two-halo contribution. Finally, we show that ongoing third-generation CMB experiments will explicitly resolve the one-halo term in low-mass groups; our methodology can be applied to these upcoming data sets to obtain a clear answer to the question of self-similarity and an improved understanding of hot gas in low-mass halos.
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We study the properties of long gamma-ray bursts (LGRBs) using a large scale hydrodynamical cosmological simulation, the Illustris simulation. We determine the LGRB host populations under different thresholds for the LGRB progenitor metallicities, according to the collapsar model. We compare the simulated sample of LGRBs hosts with recent, largely unbiased, host samples: BAT6 and SHOALS. We find that at $z<1$ simulated hosts follow the mass-metallicity relation and the fundamental metallicity relation simultaneously, but with a paucity of high-metallicity hosts, in accordance with observations. We also find a clear increment in the mean stellar mass of LGRB hosts and their SFR with redshift up to $z<3$ on account of the metallicity dependence of progenitors. We explore the possible origin of LGRBs in metal rich galaxies, and find that the intrinsic metallicity dispersion in galaxies could explain their presence. LGRB hosts present a tighter correlation between galaxy metallicity and internal metallicity dispersion compared to normal star forming galaxies. We find that the Illustris simulations favours the existence of a metallicity threshold for LGRB progenitors in the range 0.3 - 0.6 Z$_\odot$
We study galactic star-formation activity as a function of environment and stellar mass over 0.5<z<2.0 using the FourStar Galaxy Evolution (ZFOURGE) survey. We estimate the galaxy environment using a Bayesian-motivated measure of the distance to the third nearest neighbor for galaxies to the stellar mass completeness of our survey, $\log(M/M_\odot)>9 (9.5)$ at z=1.3 (2.0). This method, when applied to a mock catalog with the photometric-redshift precision ($\sigma_z / (1+z) \lesssim 0.02$), recovers galaxies in low- and high-density environments accurately. We quantify the environmental quenching efficiency, and show that at z> 0.5 it depends on galaxy stellar mass, demonstrating that the effects of quenching related to (stellar) mass and environment are not separable. In high-density environments, the mass and environmental quenching efficiencies are comparable for massive galaxies ($\log (M/M_\odot)\gtrsim$ 10.5) at all redshifts. For lower mass galaxies ($\log (M/M)_\odot) \lesssim$ 10), the environmental quenching efficiency is very low at $z\gtrsim$ 1.5, but increases rapidly with decreasing redshift. Environmental quenching can account for nearly all quiescent lower mass galaxies ($\log(M/M_\odot) \sim$ 9-10), which appear primarily at $z\lesssim$ 1.0. The morphologies of lower mass quiescent galaxies are inconsistent with those expected of recently quenched star-forming galaxies. Some environmental process must transform the morphologies on similar timescales as the environmental quenching itself. The evolution of the environmental quenching favors models that combine gas starvation (as galaxies become satellites) with gas exhaustion through star-formation and outflows ("overconsumption"), and additional processes such as galaxy interactions, tidal stripping and disk fading to account for the morphological differences between the quiescent and star-forming galaxy populations.
We explore the origin of fast molecular outflows that have been observed in Active Galactic Nuclei (AGN). Previous numerical studies have shown that it is difficult to create such an outflow by accelerating existing molecular clouds in the host galaxy, as the clouds will be destroyed before they can reach the high velocities that are observed. In this work, we consider an alternative scenario where molecules form in-situ within the AGN outflow. We present a series of hydro-chemical simulations of an isotropic AGN wind interacting with a uniform medium. We follow the time-dependent chemistry of 157 species, including 20 molecules, to determine whether molecules can form rapidly enough to produce the observed molecular outflows. We find H$_2$ outflow rates up to 140 M$_\odot$ yr$^{-1}$, which is sensitive to density, AGN luminosity, and metallicity. We compute emission and absorption lines of CO, OH and warm (a few hundred to a few thousand K) H$_2$ from the simulations in post-processing. The CO-derived outflow rates and OH absorption strengths at solar metallicity agree with observations, although the maximum line of sight velocities from the model CO spectra are a factor $\approx$2 lower than is observed. We derive a CO (1-0) to H$_2$ conversion factor of $\alpha_{\rm{CO} (1-0)}$ = 0.15 M$_\odot$ (K km s$^{-1}$ pc$^2$)$^{-1}$, 5 times lower than is commonly assumed in observations of such systems. We find strong emission from the mid-infrared lines of H$_2$, which traces at least 70 per cent of the total H$_2$ mass. This H$_2$ emission may be observable by JWST.
We present the multiwavelength photometry of two Frontier Fields massive
galaxy clusters MACS-J0717 and MACS-J1149 and their parallel fields, ranging
from HST to ground based K and Spitzer IRAC bands, and the public release of
photometric redshifts and rest frame properties of galaxies found in cluster
and parallel pointings. This work was done within ASTRODEEP project and aims to
provide a reference for future investigations of the extragalactic populations.
To fully exploit the depth of the images and detect faint sources we used an
accurate procedure which carefully removes the foreground light of bright
cluster sources and the intra-cluster light thus enabling detection and
measurement of accurate fluxes in crowded cluster regions. This same procedure
has been successfully used to derive the photometric catalogue of MACS-J0416
and Abell-2744.
The obtained multi-band photometry was used to derive photometric redshifts,
magnification and physical properties of sources. In line with the first two FF
catalogues released by ASTRODEEP, the photometric redshifts reach $\sim$4$\%$
accuracy. Moreover we extend the presently available samples to galaxies
intrinsically as faint as H160$\sim$32-34 mag thanks the magnification factors
induced to strong gravitational lensing. Our analysis allows us to probe galaxy
masses larger then 10$^{7}$ M$\odot$ and/or SFR=0.1-1M$\odot$/yr out to
redshift z$>6$.
A galaxy's orientation is one of its most basic observable properties. Astronomers once assumed that galaxies are randomly oriented in space, however it is now clear that some have preferred orientations with respect to their surroundings. Chief among these are giant elliptical galaxies found in the centers of rich galaxy clusters. Numerous studies have shown that the major axes of these galaxies often share the same orientation as the surrounding matter distribution on larger scales. Using Hubble Space Telescope observations of 65 distant galaxy clusters, we show for the first time that similar alignments are seen at earlier epochs when the universe was only one-third its current age. These results suggest that the brightest galaxies in clusters are the product of a special formation history, one influenced by development of the cosmic web over billions of years.
(Abridged version) We explore whether a scenario that combines an origin by mergers at $z\sim$1.8-1.5 with a subsequent passive evolution of the resulting S0 remnants since $z \sim$0.8-1 is compatible with observational data of S0s in the Tully-Fisher relation (TFR). We studied a set of major and minor merger experiments from the GalMer database that generate massive S0 remnants. We analysed the location of these remnants in the photometric and stellar TFRs assuming that they correspond to $z\sim0.8$ galaxies. We then estimated their evolution in these planes over the last 7 Gyr. The results were compared with data of real S0s and spirals at different redshifts. We also tested how the use of Vcirc or Vrot,max affects the results. We found that just after $\sim$1-2 Gyr of coalescence, major mergers generate S0 remnants that are outliers of the local photometric and stellar TFRs at $z\sim0.8$. After $\sim$4-7 Gyr of passive evolution in isolation, the S0 remnants move towards the local TFR, although the initial scatter among them persists. This scatter is sensitive to the indicator used for the rotation velocity: Vcirc values yield a lower scatter than when Vrot,max values are considered instead. In the planes involving Vrot,max, a clear segregation of the S0 remnants in terms of the spin-orbit coupling of the model is observed, in which the remnants of retrograde encounters overlap with local S0s hosting counter-rotating discs. The location of the S0 remnants at $z\sim 0$ agrees well with the observed distribution of local S0 galaxies in the $\sigma_0$-$M_K$, Vcirc-$\sigma_0$ and Vrot,max-$\sigma_0$ planes. Thus, massive S0 galaxies may have been formed through major mergers that occurred at high redshift and have later evolved towards the local TFR through passive evolution in relative isolation, a mechanism that would also contribute to the scatter observed in this relation.
We report ALMA observations of polarized dust emission from the protostellar source Ser-emb 8 at a linear resolution of 140 au. Assuming models of dust-grain alignment hold, the observed polarization pattern gives a projected view of the magnetic field structure in this source. Contrary to expectations based on models of strongly magnetized star formation, the magnetic field in Ser-emb 8 does not exhibit an hourglass morphology. Combining the new ALMA data with previous observational studies, we can connect magnetic field structure from protostellar core (~80,000 au) to disk (~100 au) scales. We compare our observations with four magnetohydrodynamic gravo-turbulence simulations made with the AREPO code that have initial conditions ranging from super-Alfv\'enic (weakly magnetized) to sub-Alfv\'enic (strongly magnetized). These simulations achieve the spatial dynamic range necessary to resolve the collapse of protostars from the parsec scale of star-forming clouds down to the ~100 au scale probed by ALMA. Only in the very strongly magnetized simulation do we see both the preservation of the field direction from cloud to disk scales and an hourglass-shaped field at < 1000 au scales. We conduct an analysis of the relative orientation of the magnetic field and the density structure in both the Ser-emb 8 ALMA observations and the synthetic observations of the four AREPO simulations. We conclude that the Ser-emb 8 data are most similar to the weakly magnetized simulations, which exhibit random alignment, in contrast to the strongly magnetized simulation, where the magnetic field plays a role in shaping the density structure in the source. In the weak-field case, it is turbulence -- not the magnetic field -- that shapes the material that forms the protostar, highlighting the dominant role that turbulence can play across many orders of magnitude in spatial scale.
We outline a general procedure for simulating the surface brightness of astrophysical jets (and other astronomical objects) by post-processing gas dynamical simulations of densities and temperatures using spectral line emission data from the astrophysical spectral synthesis package {\em Cloudy}. Then we validate the procedure by comparing the simulated surface brightness of the HH~30 astrophysical jet in the forbidden [O~I], [N~II], and [S~II] doublets with {\em Hubble Space Telescope}\/ observations of Hartigan and Morse and multiple-ion magnetohydrodynamic simulations of Tesileanu et al. The general trend of our simulated surface brightness in each doublet using the gas dynamical/{\em Cloudy}\/ approach is in excellent agreement with the observational data.
We developed and applied a computer analysis method to detect ring galaxy candidates in the first data release of PanSTARRS. The method works by applying a low-pass filter, followed by dynamic global thresholding to search for closed regions in the binary mask of each galaxy image. Applying the method to ~3*10^6 PanSTARRS galaxy images produced a catalog of 185 ring galaxy candidates based on their visual appearance.
We present a study comparing OVI $\lambda\lambda$1031, 1037 doublet absorption found towards group galaxy environments with that of isolated galaxies. The OVI absorption in the circumgalactic medium (CGM) of isolated galaxies has been studied previously by the "Multiphase Galaxy Halos" survey, where the kinematics and absorption properties of the CGM have been investigated. We extend these studies to group environments. We define a galaxy group to have two or more galaxies having a line-of-sight velocity difference of no more than 1000 km/s and located within 350 kpc (projected) of a background quasar sightline. We identified a total of six galaxy groups associated with OVI absorption $W_{\rm r}>0.06$ {\AA} that have a median redshift of $\langle z_{\rm gal} \rangle = 0.1669$ and a median impact parameter of $\langle D \rangle = 134.1$ kpc. An additional 12 non-absorbing groups were identified with a median redshift of $\langle z_{\rm gal} \rangle = 0.2690$ and a median impact parameter of $\langle D \rangle = 274.0$ kpc. We find the average equivalent width to be smaller for group galaxies than for isolated galaxies $(3\sigma)$. However, the covering fractions are consistent with both samples. We used the pixel-velocity two-point correlation function method and find that the velocity spread of OVI in the CGM of group galaxies is significantly narrower than that of isolated galaxies $(10\sigma)$. We suggest that the warm/hot CGM does not exist as a superposition of halos, instead, the virial temperature of the halo is hot enough for OVI to be further ionised. The remaining OVI likely exists at the interface between hot, diffuse gas and cooler regions of the CGM.
Mass, metallicity, and star formation rate (SFR) of a galaxy are crucial
parameters in understanding galaxy formation and evolution. However, the
relation among these is still a matter of debate for luminous infrared
galaxies, which carry a bulk of SFR budget of the universe at $z\sim1$. We have
investigated the relation among stellar mass, gas-phase oxygen abundance, and
SFR of AKARI-detected mid-IR galaxies at $z\sim0.88$ in the AKARI NEP deep
field. We observed about 350 AKARI sources with Subaru/FMOS NIR spectrograph,
and detected secure and expected H$\alpha$ emission lines from 25 and 44
galaxies, respectively. The SFR of our sample is almost constant ($\sim
25M_{\odot}/yr$) over the stellar mass range of our sample. Compared with
main-sequence (MS) galaxies at a similar redshift range, the average SFR of our
detected sample is comparable for massive galaxies
($\sim10^{10.58}~M_{\odot}$), while higher by $\sim$0.6dex for less massive
galaxies ($\sim 10^{10.05}~M_{\odot}$). We measure metallicities from the
[NII]/H$\alpha$ emission line ratio.
We find that the mass-metallicity relation of our individually measured
sources agrees with that for optical-selected star-forming galaxies at
$z\sim0.1$, while metallicities of stacked spectra agree with that of MS
galaxies at $z\sim0.78$. Considering high SFR of individually measured sources,
FMR of the IR galaxies is different from that at $z\sim0.1$. However, on the
mass-metallicity plane, they are consistent with the MS galaxies, highlighting
higher SFR of the IR galaxies. This suggests the evolutionary path of our IR
galaxies is different from that of MS galaxies. A possible physical
interpretation includes that the star-formation activities of IR galaxies at
$z\sim0.88$ in our sample are enhanced by interaction and/or merger of
galaxies, but the inflow of metal-poor gas is not yet induced, keeping the
metallicity intact.
We study the dynamical evolution of supermassive black holes, in the late stage of galaxy mergers, from kpc to pc scales. In particular, we capture the formation of the binary, a necessary step before the final coalescence, and trace back the main processes causing the decay of the orbit. We use hydrodynamical simulations of galaxy mergers with different resolutions, from $20\,\rm pc$ down to $1\,\rm pc$, in order to study the effects of the resolution on our results, remove numerical effects, and assess that resolving the influence radius of the orbiting black hole is a minimum condition to fully capture the formation of the binary. Our simulations include the relevant physical processes, namely star formation, supernova feedback, accretion onto the black holes and the ensuing feedback. We find that, in these mergers, dynamical friction from the smooth stellar component of the nucleus is the main process that drives black holes from kpc to pc scales. Gas does not play a crucial role and even clumps do not induce scattering or perturb the orbits. We compare the time needed for the formation of the binary to analytical predictions and suggest how to apply such analytical formalism to obtain estimates of binary formation times in lower resolution simulations.
We have identified two channels for the formation of compact dwarf galaxies in the Illustris simulation by reconstructing mass and distance histories of candidates located in the vicinity of the simulation's most massive cluster galaxies. One channel is tidal stripping of Milky Way mass galaxies that form outside of clusters and eventually sink into them, spiraling in toward central massive objects. Second channel of formation is an in-situ formation (in reference to the parent cluster) of dwarf mass galaxies, with negligible evolution and limited change in stellar mass. We find 19 compact dwarf galaxies at the centers of 14 clusters, consistent with observations. 30% of them have external origin while 70% are formed in-situ.
We analyse disc heating and radial migration in N-body models of growing disc galaxies with thick and thin discs. Similar to thin-disc-only models, galaxies with appropriate non-axisymmetric structures reproduce observational constraints on radial disc heating in and migration to the Solar Neighbourhood (Snhd). The presence of thick discs can suppress non-axisymmetries and thus higher baryonic-to-dark matter fractions are required than in models that only have a thin disc. Models that are baryon-dominated to roughly the Solar radius R_0 are favoured, in agreement with data for the Milky Way. For inside-out growing discs, today's thick-disc stars at R_0 are dominated by outwards migrators. Whether outwards migrators are vertically hotter than non-migrators depends on the radial gradient of the thick disc vertical velocity dispersion. There is an effective upper boundary in angular momentum that thick disc stars born in the centre of a galaxy can reach by migration, which explains the fading of the high-alpha sequence outside R_0. Our models compare well to Snhd kinematics from RAVE-TGAS. For such comparisons it is important to take into account the azimuthal variation of kinematics at R ~ R_0 and biases from survey selection functions. The vertical heating of thin disc stars by giant molecular clouds is only mildly affected by the presence of thick discs. Our models predict higher vertical velocity dispersions for the oldest stars than found in the Snhd age-velocity dispersion relation, possibly because of measurement uncertainties or an underestimation of the number of old cold stars in our models.
We present an analysis of far--infrared (FIR) [CII] and [OI] fine structure line and continuum observations obtained with $Herschel$/PACS, and CO(1-0) observations obtained with the IRAM Plateau de Bure Interferometer, of Lyman Break Analogs (LBAs) at $z\sim 0.2$. The principal aim of this work is to determine the typical ISM properties of $z\sim 1-2$ Main Sequence (MS) galaxies, with stellar masses between $10^{9.5}$ and $10^{11}$ $M_{\odot}$, which are currently not easily detectable in all these lines even with ALMA and NOEMA. We perform PDR modeling and apply different IR diagnostics to derive the main physical parameters of the FIR emitting gas and dust and we compare the derived ISM properties to those of galaxies on and above the MS at different redshifts. We find that the ISM properties of LBAs are quite extreme (low gas temperature, high density and thermal pressure) with respect to those found in local normal spirals and more active local galaxies. LBAs have no [CII] deficit despite having the high specific star formation rates (sSFRs) typical of starbursts. Although LBAs lie above the local MS, we show that their ISM properties are more similar to those of high-redshift MS galaxies than of local galaxies above the main sequence. This data set represents an important reference for planning future ALMA [CII] observations of relatively low-mass MS galaxies at the epoch of the peak of the cosmic star formation.
At the interface of HII regions and molecular gas peculiar structures appear, some of them with pillar-like shapes. Understanding their origin is important for characterizing triggered star formation and the impact of massive stars on the interstellar medium. In order to study the molecular environment and the influence of the radiation on two pillar-like features related to the HII region G46.5-0.2, we performed molecular line observations with the Atacama Submillimeter Telescope Experiment, and spectroscopic optical observations with the Isaac Newton Telescope. From the optical observations we identified the star that is exciting the HII region as a spectral type O4-6. The molecular data allowed us to study the structure of the pillars and a HCO+ cloud lying between them. In this HCO+ cloud, which have not any well defined 12CO counterpart, we found direct evidence of star formation: two molecular outflows and two associated near-IR nebulosities. The outflows axis orientation is perpendicular to the direction of the radiation flow from the HII region. Several Class I sources are also embedded in this HCO+ cloud, showing that it is usual that the YSOs form large associations occupying a cavity bounded by pillars. On the other hand, it was confirmed that the RDI process is not occurring in one of the pillar tips.
We combine precision radial velocity data from four different published works of the stars in the Leo II dwarf spheroidal galaxy. This yields a dataset that spans 19 years, has 14 different epochs of observation, and contains 372 unique red giant branch stars, 196 of which have repeat observations. Using this multi-epoch dataset, we constrain the binary fraction for Leo II. We generate a suite of Monte Carlo simulations that test different binary fractions using Bayesian analysis and determine that the binary fraction for Leo II ranges from $0.30^{+0.09}_{-0.10}$ to $0.34^{+0.11}_{-0.11}$, depending on the distributions of binary orbital parameters assumed. This value is smaller than what has been found for the solar neighborhood (~0.4-0.6) but falls within the wide range of values that have been inferred for other dwarf spheroidals (0.14-0.69). The distribution of orbital periods has the greatest impact on the binary fraction results. If the fraction we find in Leo II is present in low-mass ultra-faints, it can artificially inflate the velocity dispersion of those systems and cause them to appear more dark matter rich than in actuality. For a galaxy with an intrinsic dispersion of 1 km/s and an observational sample of 100 stars, the dispersion can be increased by a factor of 1.5-2 for Leo II-like binary fractions or by a factor of 3 for binary fractions on the higher end of what has been seen in other dwarf spheroidals.
Deciphering the assembly history of the Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps of the Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with a well-defined view of the current chemo-kinematical structure of the Milky Way, but will only enable a blurred view on the temporal sequence that led to the present-day Galaxy. As demonstrated by the (ongoing) exploitation of data from the pioneering photometric missions CoRoT, Kepler, and K2, asteroseismology provides the way forward: solar-like oscillating giants are excellent evolutionary clocks thanks to the availability of seismic constraints on their mass and to the tight age-initial-mass relation they adhere to. In this paper we identify five key outstanding questions relating to the formation and evolution of the Milky Way that will need precise and accurate ages for large samples of stars to be addressed, and we identify the requirements in terms of number of targets and the precision on the stellar properties that are needed to tackle such questions. By quantifying the asteroseismic yields expected from PLATO for red-giant stars, we demonstrate that these requirements are within the capabilities of the current instrument design, provided that observations are sufficiently long to identify the evolutionary state and allow robust and precise determination of acoustic-mode frequencies. This will allow us to harvest data of sufficient quality to reach a 10% precision in age. This is a fundamental pre-requisite to then reach the more ambitious goal of a similar level of accuracy, which will only be possible if we have to hand a careful appraisal of systematic uncertainties on age deriving from our limited understanding of stellar physics, a goal which conveniently falls within the main aims of PLATO's core science.
Cosmological simulations suggest that most of the matter in the Universe is distributed along filaments connecting galaxies. Illuminated by the cosmic UV background (UVB), these structures are expected to glow in fluorescent Lyman alpha emission with a Surface Brightness (SB) that is well below current observational limits for individual detections. Here, we perform a stacking analysis of the deepest MUSE/VLT data using three-dimensional regions (subcubes) with orientations determined by the position of neighbouring Lyman alpha galaxies (LAEs) at 3<z<4. Our method should increase the probability of detecting filamentary Lyman alpha emission, provided that these structures are Lyman Limit Systems (LLSs). By stacking 390 oriented subcubes we reach a 2 sigma sensitivity level of SB ~ 0.44e-20 erg/s/cm^2/arcsec^2 in an aperture of 1 arcsec^2 x 6.25 Angstrom, which is three times below the expected fluorescent Lyman alpha signal from the Haardt-Madau 2012 (HM12) UVB at z~3.5. No detectable emission is found on intergalactic scales, implying that at least two thirds of our subcubes do not contain oriented LLSs for a HM12 UVB. On the other hand, significant emission is detected in the circum-galactic medium (CGM) of galaxies in the direction of the neighbours. The signal is stronger for galaxies with a larger number of neighbours and appears to be independent of any other galaxy properties such as luminosity, redshift and neighbour distance. We estimate that preferentially oriented satellite galaxies cannot contribute significantly to this signal, suggesting instead that gas densities in the CGM are typically larger in the direction of neighbouring galaxies on cosmological scales.
The primary goal of the pulsar timing array projects is to detect ultra-low-frequency gravitational waves. The pulsar data sets are affected by numerous noise processes including varying dispersive delays in the interstellar medium and from the solar wind. The solar wind can lead to rapidly changing variations that, with existing telescopes, can be hard to measure and then remove. In this paper we study the possibility of using a low frequency telescope to aid in such correction for the Parkes Pulsar Timing Array (PPTA) and also discuss whether the ultra-wide-bandwidth receiver for the FAST telescope is sufficient to model the solar wind variations. Our key result is that a single wide-bandwidth receiver can be used to model and remove the effect of the solar wind. However, for pulsars that pass close to the Sun such as PSR J1022+1022, the solar wind is so variable that observations at two telescopes separated by a day are insufficient to correct the solar wind effect.
$\omega$ Centauri (NGC~5139) contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR) variability survey of $\omega$ Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete $J$ and $K_{\rm S}$ near-IR catalog of variable stars in the field of $\omega$ Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the fact that the amplitudes are much smaller in these bands compared to the optical. Finally, we consider the case in which all the pulsating stars in the three different variability types follow a single period-luminosity relation in the near-IR bands.
In this concluding article I recall the early history of the Gaia mission, showing that the original science case and expectations of wide community interest in Gaia data have been met. The quarter-century long partnership involving some 1,000 scientists, engineers and managers in industry and academia is delivering a large, high-quality and unique data set which will underpin astrophysics across many sub-fields for years to come.
We present a numerical simulation of the formation of a massive star using Monte- Carlo-based radiation hydrodynamics (RHD). The star forms via stochastic disc accretion and produces fast, radiation-driven bipolar cavities. We find that the evolution of the infall rate (considered to be the mass flux across a 1500 au spherical boundary), and the accretion rate onto the protostar, are broadly consistent with observational constraints. After 35kyr the star has a mass of 25 solar masses and is surrounded by a disc of mass 7 solar masses and 1500 au radius, and we find that the velocity field of the disc is close to Keplerian. Once again these results are consistent with those from recent high-resolution studies of discs around forming massive stars. Synthetic imaging of the RHD model shows good agreement with observations in the near- and far-IR, but may be in conflict with observations that suggests that MYSOs are typically circularly symmetric on the sky at 24.5 microns. Molecular line simulations of a CH3CN transition compare well with observations in terms of surface brightness and line width, and indicate that it should be possible to reliably extract the protostellar mass from such observations.
Context. The first generation of stars formed in the Galaxy left behind the chemical signatures of their nucleosynthesis in the interstellar medium, visible today in the atmospheres of low-mass stars formed afterwards. Sampling the chemistry of low-mass provides insight into the first stars. Aims. We aim to increase the samples of stars with extremely low metal abundances, identifying ultra metal-poor stars from spectra with modest spectral resolution and signal-to-noise ratio (S/N). Achieving this goal involves deriving reliable metallicities and carbon abundances from such spectra. Methods. We carry-out follow-up observations of faint, V>19, metal-poor candidates selected from SDSS spectroscopy and observed with OSIRIS at GTC. The SDSS and follow-up OSIRIS spectra have been analyzed using the FERRE code to derive effective temperatures, surface gravities, metallicities and carbon abundances. In addition, a well-known extremely metal-poor star has been included in our sample to calibrate the analysis methodology. Results. We have observed and analyzed five metal-poor candidates from modest-quality SDSS spectra. All stars in our sample have been confirmed as extremely metal-poor stars, in the [Fe/H]<-3.3 regime. We report the recognition of J173403+644632, a carbon-enhanced ultra metal-poor dwarf star with [Fe/H]=-4.3 and [C/Fe]=+3.1.
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We use the timescale distribution of ~3000 microlensing events measured by the OGLE-III survey, together with accurate new made-to-measure dynamical models of the Galactic bulge/bar region, to measure the IMF in the inner Milky Way. The timescale of each event depends on the mass of the lensing object, together with the relative distances and velocities of the lens and source. The dynamical model provides statistically these distances and velocities allowing us to constrain the lens mass function, and from this to infer the IMF. Parameterising the IMF as a broken power-law, we find slopes in the main sequence $\alpha_{\rm ms}=1.31\pm0.10|_{\rm stat}\pm0.10|_{\rm sys}$ and brown dwarf region $\alpha_{\rm bd}=-0.7\pm0.9|_{\rm stat}\pm0.8|_{\rm sys}$ where we use a fiducial 50% binary fraction, and the systematic uncertainty covers the range of binary fractions 0-100%. Similarly for a log-normal IMF we conclude $M_c=(0.17\pm0.02|_{\rm stat}\pm0.01|_{\rm sys})M_\odot$ and $\sigma_m=0.49\pm0.07|_{\rm stat}\pm0.06|_{\rm sys}$. These values are very similar to a Kroupa or Chabrier IMF respectively, showing that the IMF in the bulge is indistinguishable from that measured locally, despite the lenses lying in the inner Milky Way where the stars are mostly ~10Gyr old and formed on a fast $\alpha$-element enhanced timescale. This therefore constrains models of IMF variation that depend on the properties of the collapsing gas cloud.
Large samples of globular clusters (GC) with precise multi-wavelength photometry are becoming increasingly available and can be used to constrain the formation history of galaxies. We present the results of an analysis of Milky Way (MW) and Virgo core GCs based on five optical-near-infrared colors and ten synthetic stellar population models. For the MW GCs, the models tend to agree on photometric ages and metallicities, with values similar to those obtained with previous studies. When used with Virgo core GCs, for which photometry is provided by the Next Generation Virgo cluster Survey (NGVS), the same models generically return younger ages. This is a consequence of the systematic differences observed between the locus occupied by Virgo core GCs and models in panchromatic color space. Only extreme fine-tuning of the adjustable parameters available to us can make the majority of the best-fit ages old. Although we cannot exclude that the formation history of the Virgo core may lead to more conspicuous populations of relatively young GCs than in other environments, we emphasize that the intrinsic properties of the Virgo GCs are likely to differ systematically from those assumed in the models. Thus, the large wavelength coverage and photometric quality of modern GC samples, such as used here, is not by itself sufficient to better constrain the GC formation histories. Models matching the environment-dependent characteristics of GCs in multi-dimensional color space are needed to improve the situation.
We study star formation within outflows driven by active galactic nuclei (AGN) as a new source of hypervelocity stars (HVSs). Recent observations revealed active star formation inside a galactic outflow at a rate of $\sim 15\,M_{\odot}\,\rm yr^{-1}$. We show that the shells swept up by an AGN outflow are capable of cooling and fragmentation into cold clumps embedded in a hot tenuous gas via thermal instabilities. As a result, stars are produced along outflow's path, endowed with the outflow speed at their formation site. These HVSs travel through the galactic halo and eventually escape into the intergalactic medium. The expected instantaneous rate of star formation inside the outflow is $\sim 4-5$ orders of magnitude greater than the average rate associated with previously proposed mechanisms for producing HVSs, such as the Hills mechanism and three-body interaction between a star and a black hole binary.
The significant diversity of rotation curve (RC) shapes in dwarf galaxies has recently emerged as a challenge to LCDM: in dark matter (DM) only simulations, DM halos have a universal cuspy density profile that results in self-similar RC shapes. We compare RC shapes of simulated galaxies from the NIHAO project with observed galaxies from the homogeneous SPARC dataset. The DM halos of the NIHAO galaxies can expand to form cores, with the degree of expansion depending on their stellar-to-halo mass ratio. By means of the V$_{\rm 2kpc}$--V$_{\rm Rlast}$ relation (where V$_{\rm Rlast}$ is the outermost measured rotation velocity), we show that both the average trend and the scatter in RC shapes of NIHAO galaxies are in reasonable agreement with SPARC: this represents a significant improvement compared to simulations that do not result in DM core formation, showing that halo expansion is a key process in matching the diversity of dwarf galaxy RCs. Note that NIHAO galaxies can reproduce even the extremely slowly rising RCs of IC2574 and UGC5750. Revealingly, the range where observed galaxies show the highest diversity corresponds to the range where core formation is most efficient in NIHAO simulations, 60$<$V$_{\rm Rlast}$/km/s$<$100. A few observed galaxies in this range cannot be matched by any NIHAO RC nor by simulations that predict a universal halo profile. Interestingly, the majority of these are starbursts or emission-line galaxies, with steep RCs and small effective radii. Such galaxies represent an interesting observational target providing new clues to the process/viability of cusp-core transformation, the relationship between starburst and inner potential well, and the nature of DM.
Studying the coupling between the energy output produced by the central quasar and the host galaxy is fundamental to fully understand galaxy evolution. Quasar feedback is indeed supposed to dramatically affect the galaxy properties by depositing large amounts of energy and momentum into the ISM. In order to gain further insights on this process, we study the SEDs of sources at the brightest end of the quasar luminosity function, for which the feedback mechanism is supposed to be at its maximum. We model the rest-frame UV-to-FIR SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6 disentangling the different emission components and deriving physical parameters of both the nuclear component and the host galaxy. We also use a radiative transfer code to account for the contribution of the quasar-related emission to the FIR fluxes. Most SEDs are well described by a standard combination of accretion disk+torus and cold dust emission. However, about 30% of them require an additional emission component in the NIR, with temperatures peaking at 750K, which indicates the presence of a hotter dust component in these powerful quasars. We measure extreme values of both AGN bolometric luminosity (LBOL > 10^47 erg/s) and SFR (up to 2000 Msun/yr). A new relation between quasar and star-formation luminosity is derived (LSF propto LQSO^(0.73)) by combining several Herschel-detected quasar samples from z=0 to 4. Future observations will be crucial to measure the molecular gas content in these systems, probe the impact between quasar-driven outflows and on-going star-formation, and reveal the presence of merger signatures in their host galaxies.
As astronomers increasingly exploit the information available in the time domain, spectroscopic variability in particular opens broad new channels of investigation. Here we describe the selection algorithms for all targets intended for repeat spectroscopy in the Time Domain Spectroscopic Survey (TDSS), part of the extended Baryon Oscillation Spectroscopic Survey within the Sloan Digital Sky Survey-IV. Also discussed are the scientific rationale and technical constraints leading to these target selections. The TDSS includes a large "Repeat Quasar Spectroscopy" (RQS) program delivering ~13,000 repeat spectra of confirmed SDSS quasars, and several smaller "Few-Epoch Spectroscopy" (FES) programs targeting specific classes of quasars as well as stars. The RQS program aims to provide a large and diverse quasar data set for studying variations in quasar spectra on timescales of years, a comparison sample for the FES quasar programs, and opportunity for discovering rare, serendipitous events. The FES programs cover a wide variety of phenomena in both quasars and stars. Quasar FES programs target broad absorption line quasars, high signal-to-noise ratio normal broad line quasars, quasars with double-peaked or very asymmetric broad emission line profiles, binary supermassive black hole candidates, and the most photometrically variable quasars. Strongly variable stars are also targeted for repeat spectroscopy, encompassing many types of eclipsing binary systems, and classical pulsators like RR Lyrae. Other stellar FES programs allow spectroscopic variability studies of active ultracool dwarf stars, dwarf carbon stars, and white dwarf/M dwarf spectroscopic binaries. We present example TDSS spectra and describe anticipated sample sizes and results.
A new deep HI survey of the galaxy Messier 33 is presented, based on observations obtained at the Dominion Radio Astrophysical Observatory. We observe a perturbed outer gas distribution and kinematics in M33, and confirm the disk warping as a significant kinematical twist of the major axis of the velocity field, though no strong tilt is measured, in agreement with previous work. Evidence for a new low brightness HI component with anomalous velocity is reported. It harbours a large velocity scatter, as its kinematics both exceeds and lags the rotation of the disk, and leaks in the forbidden velocity zone of apparent counter-rotation. The observations also reveal wide and multiple peak HI profiles which can be partly explained by crowded orbits in the framework of the warp model. Asymmetric motions are identified in the velocity field, as possible signatures of a lopsided potential and the warp. The mass distribution modeling of the hybrid Halpha-HI rotation curve favours a cuspy dark matter halo with a concentration in disagreement with the LambdaCDM dark halo mass-concentration relationship. The total mass enclosed in 23 kpc is 8 10^10 Msol, of which 11% are stars and gas. At the virial radius of the cuspy halo, the resulting total mass is 5 10^11 Msol, but with a baryonic mass fraction of 2% only. This strongly suggests a more realistic radius encompassing the total mass of M33 well smaller than the virial radius of the halo, maybe comparable to the size of the HI disk.
We report on the detection of two Ne VIII absorbers, at z = 0.61907 and z = 0.57052 in the HST/COS spectrum of background quasars SDSS J 080908.13+461925.6 and SBS 1122+594 respectively. The Ne VIII 770 line is at $\sim 3\sigma$ significance. In both instances, the NeVIII is found to be tracing gas with $T \gtrsim 10^5$ K, predominantly collisionally ionized, with moderate densities of $n_{H} \lesssim 10^{-4}$ $cm^{-3}$, sub-solar metallicities and total hydrogen column densities of $N(H) \gtrsim 10^{19}$ $cm^{2}$. In the z = 0.61907 absorber, the low, intermediate ions and O VI are consistent with origin in photoionized gas, with the O VI potentially having some contribution from the warm collisional phase traced by Ne VIII. The z = 0.57052 system has H I absorption in at least three kinematically distinct components, with one of them having $b (H I) = 49 {\pm} 11$ $km s^{-1}$. The intermediate ionization lines, O VI and Ne VIII are coincident in velocity with this component. Their different line widths suggest warm temperatures of $T = (0.5 - 1.5) \times 10^5$ K. Both absorbers are residing in regions where there are several luminous ($ \gtrsim L^*$) galaxies. The absorber at z = 0.57052 is within the virial radius of a $2.6L^*$ galaxy, possibly associated with shock heated circumgalactic material.
We present the results from a multiwavelength study of the flaring activity in HBL, 1ES 1959+650, during January 2015-June 2016. The source underwent significant flux enhancements showing two major outbursts (March 2015 and October 2015) in optical, UV, X-rays and gamma-rays. Normally, HBLs are not very active but 1ES 1959+650 has shown exceptional outburst activity across the whole electromagnetic spectrum (EMS). We used the data from Fermi-LAT, Swift-XRT & UVOT and optical data from Mt. Abu InfraRed Observatory (MIRO) along with archival data from Steward Observatory to look for possible connections between emissions at different energies and the nature of variability during flaring state. During October 2015 outburst, thirteen nights of optical follow-up observations showed brightest and the faintest nightly averaged V-band magnitudes as 14.45(0.03) and 14.85(0.02), respectively. In optical, the source showed a hint of optical intra-night variability during the outburst. A significant short-term variability in optical during MJD 57344 to MJD 57365 and in gamma-rays during MJD 57360 and MJD 57365 was also noticed. Multiwavelength study suggests the flaring activity at all frequencies to be correlated in general, albeit with diverse flare durations. We estimated the strength of the magnetic field as 4.21 G using the time-lag between optical and UV bands as synchrotron cooling time scale (2.34 hrs). The upper limits on the sizes of both the emission regions, gamma-ray and optical, are estimated to be of the order of 10^16cm using shortest variability time scales. The quasi-simultaneous flux enhancements in 15 GHz and VHE gamma-ray emissions indicates to a fresh injection of plasma into the jet, which interacts with a standing sub-mm core resulting in co-spatial emissions across the EMS. The complex and prolonged behavior of the second outburst in October 2015 is discussed in detail.
We investigate the stellar masses of the class of star-forming objects known as Luminous Compact Blue Galaxies (LCBGs) by studying a sample of galaxies in the distant cluster MS$~$0451.6-0305 at $z\approx0.54$ with ground-based multicolor imaging and spectroscopy. For a sample of 16 spectroscopically-confirmed cluster LCBGs (colour $B-V < 0.5$, surface brightness $\mu_B < 21$ mag arcsec$^{-2}$, and magnitude $M_B < -18.5$), we measure stellar masses by fitting spectral energy distribution (SED) models to multiband photometry, and compare with dynamical masses (determined from velocity dispersion between 10 $<$ $\sigma_v (\rm km~ s^{-1})$ $<$ 80), we previously obtained from their emission-line spectra. We compare two different stellar population models that measure stellar mass in star-bursting galaxies, indicating correlations between the stellar age, extinction, and stellar mass derived from the two different SED models. The stellar masses of cluster LCBGs are distributed similarly to those of field LCBGs, but the cluster LCBGs show lower dynamical-to-stellar mass ratios ($\rm M_{dyn}/M_{\ast} = 2.6$) than their field LCBG counterparts ($\rm M_{dyn}/M_{\ast}=4.8$), echoing trends noted previously in low-redshift dwarf elliptical galaxies. Within this limited sample, the specific star formation rate declines steeply with increasing mass, suggesting that these cluster LCBGs have undergone vigorous star formation.
We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e. a system expected to be old and relaxed long after the giant elliptical galaxy assembly. Instead, the Chandra data reveal that the hot gas morphology is disturbed and asymmetrical, with a cold front following a possible bow shock. We discuss possible origins of the disturbed hot halo, including sloshing by a nearby galaxy, ram pressure by external hotter gas, merger and nuclear outburst. We consider that a minor merger with a low impact parameter is the most likely origin: NGC 1132 may be a rare example of unusual late mergers seen in recent simulations. Regardless of the origin of the disturbed hot halo, the paradigm of the fossil system needs to be reconsidered.
If a component of dark matter has dissipative interactions, it can cool to form compact astrophysical objects with higher density than that of conventional cold dark matter (sub)haloes. Dark matter annihilations might then appear as point sources, leading to novel morphology for indirect detection. We explore dissipative models where interaction with the Standard Model might provide visible signals, and show how such objects might give rise to the observed excess in gamma rays arising from the galactic center.
As a result of the search for the identity of the chromophores responsible for producing the diffuse interstellar bands, a comprehensive exposition of experimental data is presented, which implicates the following molecules- 1. The extremely stable organic molecules, magnesium tetrabenzoporphyrin (MgTBP) and H2TBP. 2. A paraffin matrix (referred to as grains) containing TBPs. 3. A low concentration of pyridine (also within the grains), whose transmission window at 2175 Angstroms, accounts for the ubiquitous UV bump. The blue emission spectra associated with the central star, HD44179, of the Red Rectangle displays the fluorescence excitation spectra of bare MgTBP. This unique spectrum matches the low temperature lab data of MgTBP in the vapor phase. An effective grain temperature of 2.728 K (plus or minus 0.008) was deduced, based on MgTBPs lowest measured vibrational state of 341 GHz.
We report the discovery of 11 very faint (r< 23), low surface brightness ({\mu}_r< 27 mag/arcsec^2) dwarf galaxies in one deep field in the Virgo cluster, obtained by the prime focus cameras (LBC) at the Large Binocular Telescope (LBT). These extend our previous sample to reach a total number of 27 galaxies in a field of just of 0.17 deg^2 located at a median distance of 390 kpc from the cluster center. Their association with the Virgo cluster is supported by their separate position in the central surface brightness - total magnitude plane with respect to the background galaxies of similar total magnitude. For a significant fraction (26\%) of the sample the association to the cluster is confirmed by spectroscopic follow-up. We show that the mere abundance of satellite galaxies corresponding to our observed number in the target field provides extremely tight constraints on Dark Matter models with suppressed power spectrum compared to the Cold Dark Matter case, independently of the galaxy luminosity distribution. In particular, requiring the observed number of satellite galaxies not to exceed the predicted abundance of Dark Matter sub-halos yields a limit m_X >3 keV at 1-{\sigma} and m_X > 2.3 keV at 2-{\sigma} confidence level for the mass of thermal Warm Dark Matter particles. Such a limit is competitive with other limits set by the abundance of ultra-faint satellite galaxies in the Milky Way, is completely independent of baryon physics involved in galaxy formation, and has the potentiality for appreciable improvements with next observations. We extend our analysis to Dark Matter models based on sterile neutrinos, showing that our observations set tight constraints on the combination of sterile neutrino mass m_{\nu} and mixing parameter sin^2(2{\theta}). We discuss the robustness of our results with respect to systematics.
We perform three-dimensional radiation non-ideal magnetohydrodynamics simulations and investigate the impact of the Hall effect on the angular momentum evolution in the collapsing cloud cores in which the magnetic field $\mathbf{B}$ and angular momentum $\mathbf{J_{\rm ang}}$ are misaligned each other. We find that the Hall effect notably changes the magnetic torques in the pseudo-disk, and strengthens and weakens the magnetic braking in cores with an acute and obtuse relative angles between $\mathbf{B}$ and $\mathbf{J_{\rm ang}}$, respectively. This suggests that the bimodal evolution of the disk size may appear in Class 0 young stellar objects (YSOs) even if $\mathbf{B}$ and $\mathbf{J_{\rm ang}}$ are randomly distributed. We show that a counter-rotating envelope form in the upper envelope of the pseudo-disk in cloud cores with obtuse relative angles. We also find that a counter-rotating region forms at the midplane of the pseudo-disk in cloud cores with acute relative angles. The former and latter types of counter-rotating envelopes may be associated with the YSOs with a large ($r\sim100$ AU) and small ($r\lesssim10$ AU) disks, respectively.
We discuss the generic properties of any general mass distribution $\mathcal{D}(r,\theta)$ depending on one parameter $\theta$ and endowed with spherical symmetry. We show (a) that the de Sitter behavior of spacetime at the origin is generic and depends only on $\mathcal{D}(0,\theta)$, (b) that, due to the character of the cumulative distribution of $\mathcal{D}(r,\theta)$, the geometry may posses up to two horizons depending solely on the value of the total mass $M$, and (c) that no scalar invariant nor a thermodynamic entity diverges. We define new two-parameter mathematical distributions mimicking Gaussian and step-like functions and reduce to the Dirac distribution in the limit of vanishing parameter $\theta$. We use these distributions to derive in closed forms asymptotically flat, spherically symmetric, solutions that describe and model a variety of physical and geometric entities ranging from noncommutative black holes, quantum-corrected black holes to stars and dark matter halos for various scaling values of $\theta$. We show that the linear mass density $\pi c^2/G$ is an upper limit for regular-black-hole formation.
We have monitored the BL Lacertae object S5 0716+714 in the optical bands during 2012 January and February with long time spans on intraday timescales ($>$5 hr) and high time resolutions. During this monitoring period, the object shows violent flaring activity both in short and intraday timescales. The object has high value of duty cycle. The light curves detected as intraday variability (IDV) show variability of various shapes. The variability amplitude is from 12.81 per cent to 33.22 per cent, and the average value $19.92\pm5.87$ per cent. The overall magnitude variabilities are $\bigtriangleup B=1^{\rm m}.24$, $\bigtriangleup V=1^{\rm m}.42$, $\bigtriangleup R=1^{\rm m}.3$, $\bigtriangleup I=1^{\rm m}.23$ respectively. During the observations, the average change rate is $<CR>=0.035\pm0.009$ Mag/h during the ascent and $<CR>=0.035\pm0.014$ Mag/h during the descent. However, different cases are found on certain nights. There are good inter-bands correlations but not significant time lags for intraday and short timescales. The results of the autocorrelation function show that the variability timescales range from 0.054 day to 0.134 day. Most of nights show bluer when brighter (BWB) chromatic trend; a weak redder with brighter (RWB) trend is found; a few nights show no correlations between magnitude and color index. The BWB trend appears in the short timescales. During the flare the spectral index exhibits a clockwise loop for inter-nights. A shock-in-jet model and the shock wave propagating along a helical path are likely to explain the variability and color index variability.
Protoplanetary disks are thought to have lifetimes of $3-6$ million years in the solar neighborhood, but recent observations suggest that the disk lifetimes are shorter in a low metallicity environment. We perform a suite of radiation hydrodynamics simulations of photoevaporation of protoplanetary disks to study the disk structure and its long-term evolution of $\sim 10000$ years, and the metallicity dependence of mass-loss rate. Our simulations follow hydrodynamics, extreme and far ultraviolet radiative transfer, and non-equilibrium chemistry in a self-consistent manner. Dust grain temperatures are also calculated consistently by solving the radiative transfer of the stellar irradiation and grain (re-)emission. We vary the disk gas metallicity over a wide range of $10^{-4} Z_\odot \leq Z \leq 10~Z_\odot$. For our fiducial model with a 0.5 $M_\odot$ central star with solar metallicity, the time-averaged photoevaporation rate is $\dot{M}_{\rm ph} = 1.38 \times 10^{-8} M_\odot {\rm yr}^{-1}$. The photoevaporation rate is lower with higher metallicity in the range of $10^{-0.5} Z_\odot \lesssim Z \lesssim 10~Z_\odot$, because dust shielding effectively prevents far-ultra violet (FUV) photons from penetrating into and heating the dense regions of the disk. The photoevaporation rate sharply declines at even lower metallicities in $10^{-1} Z_\odot \lesssim Z \lesssim 10^{-0.5} Z_\odot$, because FUV photoelectric heating is not efficient any more to raise the gas temperature and to drive outflows. At $10^{-4} Z_\odot \leq Z \lesssim 10^{-1} Z_\odot$, HI photoionization heating acts as a dominant gas heating process and drives photoevaporative flows with roughly a constant rate. The typical disk lifetime is shorter at $Z=0.3~Z_\odot$ than at $Z = Z_\odot$, being consistent with recent observations of the extreme outer galaxy. (abridged)
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We report on the discovery of three especially bright candidate $z_{phot} \gtrsim 8$ galaxies. Five sources were targeted for follow-up with HST/WFC3, selected from a larger sample of 16 bright ($24.8 \lesssim H\lesssim25.5$~mag) candidate $z\gtrsim 8$ LBGs identified over the 1.6 degrees$^2$ of the COSMOS/UltraVISTA field. These were identified as $Y$ and $J$ dropouts by leveraging the deep ($Y$-to-$K_\mathrm{S} \sim 25.6-25.2$~mag, $5\sigma$) NIR data from the UltraVISTA DR3 release, deep ground based optical imaging from the CFHTLS and Subaru Suprime Cam programs and Spitzer/IRAC mosaics combining observations from the SMUVS and SPLASH programs. Through the refined spectral energy distributions, which now also include new HyperSuprime Cam $g, r, i, z,$ and $Y$ band data, we confirm that 3/5 galaxies have robust $z_{phot}\sim8.0-8.7$, consistent with the initial selection. The remaining 2/5 galaxies have a nominal $z_{phot}\sim2$. However, if we use the HST data alone, these objects have increased probability of being at $z\sim9$. Furthermore, we measure mean UV continuum slopes $\beta=-1.97\pm0.23$ for the three $z\sim8-9$ galaxies, marginally bluer than similarly luminous $z\sim4-6$ in CANDELS but consistent with previous measurements of similarly luminous galaxies at $z \sim 7$. The circularized effective radius for our brightest source is $0.9\pm0.2$ kpc, consistent with previous measurements for a bright $z\sim11$ galaxy and bright $z\sim7$ galaxies. Finally, using the $1/V_\mathrm{max}$ formalism, we estimate for the first time the volume density of the extreme bright ($M_\mathrm{UV}\lesssim -22$~mag) end of the $z\sim8$ UV LF from actual detection of sources, as opposed to current upper limits from non-detections. Despite this exceptional result, the still large statistical uncertainties do not allow us to discriminate between a Schechter and a double power-law form.
The earliest galaxies are expected to emerge in the first billion years of the Universe during the Epoch of Reionization. However, both the spectroscopic confirmation of photometrically-selected galaxies at this epoch and the characterization of their early dynamical state has been hindered by the lack of bright, accessible lines to probe the velocity structure of their interstellar medium. We present the first ALMA spectroscopic confirmation of such sources at z > 6 using the far-infrared [C II]{\lambda}157.74{\mu}m emission line, and, for the first time, measurement of the velocity structure, for two galaxies at z = 6.8540+/-0.0003 and z = 6.8076+/-0.0002. Remarkably, the [C II] line luminosity from these galaxies is higher than previously found in `normal' star-forming galaxies at z > 6.5. This suggests that we are sampling a part of the galaxy population different from the galaxies found through detection of the Ly{\alpha} line. The luminous and extended [C II] detections reveal clear velocity gradients that, if interpreted as rotation, would suggest these galaxies have turbulent, yet rotation-dominated disks, with similar stellar-to-dynamical mass fractions as observed for H{\alpha} emitting galaxies 2 Gyr later at cosmic noon. Our novel approach for confirming galaxies during Reionization paves the way for larger studies of distant galaxies with spectroscopic redshifts from ALMA. Particularly important, this opens up opportunities for high angular-resolution [C II] dynamics in galaxies less than one billion years after the Big Bang.
Recent work has studied the interplay between a galaxy's history and its observable properties using "genetically modified" cosmological zoom simulations. The approach systematically generates alternative histories for a halo, while keeping its cosmological environment fixed. Applications to date altered linear properties of the initial conditions such as the mean overdensity of specified regions; we extend the formulation to include quadratic features such as local variance, which determines the overall importance of smooth accretion relative to mergers in a galaxy's history. We introduce an efficient algorithm for this new class of modification and demonstrate its ability to control the variance of a region in a one-dimensional toy model. Outcomes of this work are two-fold: (i) a clarification of the formulation of genetic modifications and (ii) a proof of concept for quadratic modifications leading the way to a forthcoming implementation in cosmological simulations.
Thin, magnetically aligned striations of relatively moderate contrast with the background are commonly observed in both atomic and molecular clouds. They are also prominent in MHD simulations with turbulent converging shocks. The simulated striations develop within a dense, stagnated sheet in the mid plane of the post-shock region where magnetically-induced converging flows collide. We show analytically that the secondary flows are an inevitable consequence of the jump conditions of oblique MHD shocks. They produce the stagnated, sheet-like sub-layer through a secondary shock when, roughly speaking, the Alfv\'enic speed in the primary converging flows is supersonic, a condition that is relatively easy to satisfy in interstellar clouds. The dense sub-layer is naturally threaded by a strong magnetic field that lies close to the plane of the sub-layer. The substantial magnetic field makes the sheet highly anisotropic, which is the key to the striation formation. Specifically, perturbations of the primary inflow that vary spatially perpendicular to the magnetic field can easily roll up the sheet around the field lines without bending them, creating corrugations that appear as magnetically-aligned striations in column density maps. On the other hand, perturbations that vary spatially along the field lines curve the sub-layer and alter its orientation relative to the magnetic field locally, seeding special locations that become slanted overdense filaments and prestellar cores through enhanced mass accumulation along field lines. In our scenario, the dense sub-layer unique to magnetized oblique shocks is the birthplace for both magnetically-aligned diffuse striations and massive star-forming structures.
Understanding how QSO's UV radiation affects galaxy formation is vital to our understanding of reionization era. Using a custom made narrow-band filter, $NB906$, on Subaru/Suprime-Cam, we investigated the number density of Ly$\alpha$ emitters (LAE) around a QSO at z=6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field-of-view of Suprime-Cam, our survey area is $\sim$5400~cMpc$^2$, much larger than previously studies at z=5.7 ($\sim$200 cMpc$^2$). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies (LBGs). Based on this, we expected to detect $\sim$100 LAEs down to $NB906$=25 ABmag. However, our 6.4 hour exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 $p$Mpc across. A simple argument suggests a strong UV radiation from the QSO can suppress star-formation in halos with $M_{vir}<10^{10}M_{\odot}$ within a $p$Mpc from the QSO, but the deficit at the edge of the field (5 $p$Mpc) remains to be explained.
We present subarcsecond 1.3 mm continuum ALMA observations towards the Orion Molecular Cloud 1 South (OMC-1S) region, down to a spatial resolution of 100 AU. The observations reveal a total of 31 continuum sources, which are grouped in cores along three main filaments, with the cores being separated about 2000 AU in the filaments. We also present subarcsecond 7 mm continuum VLA observations of the same region, which allow to further study fragmentation in each core down to a spatial resolution of 40 AU. Typical separations between fragments are <560 AU and about 2900 AU, suggesting a two-level fragmentation process. In addition, a higher fragmentation level is clearly found towards the southern filament, which is the one enclosing a higher mass (higher density) within 1000 AU per each fragmenting core. This is fully consistent with previous studies of fragmentation at spatial scales one order of magnitude larger, and suggests that fragmentation down to 40 AU seems to be governed by thermal Jeans processes in OMC-1S.
Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements, because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically-enriched outflows or in more chemically-pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities . Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.
IC342 is a nearby, late-type spiral galaxy with a young nuclear star cluster surrounded by several giant molecular clouds. The IC342 nuclear region is similar to the Milky Way and therefore provides an interesting comparison. We explore star formation in the nucleus using radio recombination line (RRL) and continuum emission at 5, 6.7, 33, and 35 GHz with the JVLA. These radio tracers are largely unaffected by dust and therefore sensitive to all of the thermal emission from the ionized gas produced by early-type stars. We resolve two components in the RRL and continuum emission within the nuclear region that lie east and west of the central star cluster. These components are associated both spatially and kinematically with two giant molecular clouds. We model these regions in two ways: a simple model consisting of uniform gas radiating in spontaneous emission, or as a collection of many compact HII regions in non-LTE. The multiple HII region model provides a better fit to the data and predicts many dense (ne ~ 10^4-10^5 cm-3), compact (< 0.1 pc) HII regions. For the whole nuclear region as defined by RRL emission, we estimate a hydrogen ionizing rate of NL ~ 2 x 10^{52} s^{-1}, corresponding to equivalent ~ 2000 O6 stars and a star formation rate of ~ 0.15 Msun/year. We detect radio continuum emission west of the southern molecular mini spiral arm, consistent with trailing spiral arms.
We use the Spitzer SAGE survey of the Magellanic Clouds to evaluate the relationship between the 8-mic PAH emission, 24-mic hot dust emission, and HII region radiative transfer. We confirm that in the higher-metallicity Large Magellanic Cloud, PAH destruction is sensitive to optically thin conditions in the nebular Lyman continuum: objects identified as optically thin candidates based on nebular ionization structure show 6 times lower median 8-mic surface brightness (0.18 mJy arcsec^-2) than their optically thick counterparts (1.2 mJy arcsec^-2). The 24-mic surface brightness also shows a factor of 3 offset between the two classes of objects (0.13 vs 0.44 mJy arcsec^-2, respectively), which is driven by the association between the very small dust grains and higher density gas found at higher nebular optical depths. In contrast, PAH and dust formation in the low-metallicity Small Magellanic Cloud is strongly inhibited such that we find no variation in either 8-mic or 24-mic emission between our optically thick and thin samples. This is attributable to extremely low PAH and dust production together with high, corrosive UV photon fluxes in this low-metallicity environment. The dust mass surface densities and gas-to-dust ratios determined from dust maps using Herschel HERITAGE survey data support this interpretation.
Recent observations near the Galactic Centre have found several molecular filaments displaying striking helically-wound morphology, which are collectively known as "molecular tornadoes." We investigate the equilibrium structure of these molecular tornadoes by formulating a magnetohydrodynamic model of a rotating, helically magnetized filament. A special analytical solution is derived where centrifugal forces balance exactly with toroidal magnetic stress. From the physics of torsional Alfv\'{e}n waves, we derive a constraint that links the toroidal flux-to-mass ratio and the pitch angle of the helical field to the rotation laws, which we find to be an important component in describing molecular tornado structure. The models are compared to the Ostriker solution for isothermal, non-magnetic, non-rotating filaments. We find that neither the analytic model nor the Alfv\'{e}n wave model suffer from unphysical density inversions noted by other authors. A Monte Carlo exploration of our parameter space is constrained by observational measurements of the Pigtail Molecular Cloud (Pigtail), Double Helix Nebula (DHN), and Galactic Centre molecular Tornado (GCT). Observable properties such as the velocity dispersion, filament radius, linear mass, and surface pressure can be used to derive three dimensionless constraints for our dimensionless models of these three objects. A virial analysis of these constrained models is studied for these three molecular tornadoes. We find that self-gravity is relatively unimportant, whereas magnetic fields, and external pressure play a dominant role in the confinement and equilibrium radial structure of these objects.
We investigate the energy sources of random turbulent motions of ionised gas
from H$\alpha$ emission in eight local star-forming galaxies from the
Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. These
galaxies satisfy strict pure star-forming selection criteria to avoid
contamination from active galactic nuclei (AGN) or strong shocks/outflows.
Using the relatively high spatial and spectral resolution of SAMI, we find that
-- on sub-kpc scales our galaxies display a flat distribution of ionised gas
velocity dispersion as a function of star formation rate (SFR) surface density.
A major fraction of our SAMI galaxies shows higher velocity dispersion than
predictions by feedback-driven models, especially at the low SFR surface
density end.
Our results suggest that additional sources beyond star formation feedback
contribute to driving random motions of the interstellar medium (ISM) in
star-forming galaxies. We speculate that gravity, galactic shear, and/or
magnetorotational instability (MRI) may be additional driving sources of
turbulence in these galaxies.
We present a study of AGN feedback at higher redshifts ($0.3<z<1.2$) using Sunyaev-Zel'dovich (SZ) selected samples of clusters from the South-Pole Telescope and Atacama Cosmology Telescope surveys. In contrast to studies of nearby systems, we do not find a separation between cooling flow clusters and non-cooling flow clusters based on the radio luminosity of the central radio source. This lack may be due to the increased incidence of galaxy-galaxy mergers at higher redshift that triggers AGN activity. In support of this scenario, we find evidence for evolution in the radio luminosity function of the central radio source: while the lower-luminosity sources do not evolve much, the higher-luminosity sources show a strong increase in the frequency of their occurrence at higher redshifts. We interpret this evolution as an increase in high-excitation radio galaxies (HERGs) in massive clusters at $z>0.6$, implying a transition from HERG-mode accretion to lower-power low-excitation radio galaxy (LERG)-mode accretion at intermediate redshifts. Additionally, we use local radio-to-jet power scaling relations to estimate feedback power and find that half of the cooling flow systems in our sample probably have enough heating to balance cooling. However, we postulate that the local relations are likely not well suited to predict feedback power in high-luminosity HERGs, as they are derived from samples composed mainly of lower-luminosity LERGs.
Combining large-area optical quasar surveys with the new far-infrared Herschel-ATLAS Data Release 1, we search for an observational signature associated with the minority of quasars possessing bright far-infrared (FIR) luminosities. We find that FIR-bright quasars show broad CIV emission line blueshifts in excess of that expected from the optical luminosity alone, indicating particularly powerful nuclear outflows. The quasars show no signs of having redder optical colours than the general ensemble of optically-selected quasars, ruling out differences in line-of-sight dust within the host galaxies. We postulate that these objects may be caught in a special evolutionary phase, with unobscured, high black hole accretion rates and correspondingly strong nuclear outflows. The high FIR emission found in these objects is then either a result of star formation related to the outflow, or is due to dust within the host galaxy illuminated by the quasar. We are thus directly witnessing coincident small-scale nuclear processes and galaxy-wide activity, commonly invoked in galaxy simulations which rely on feedback from quasars to influence galaxy evolution.
We discovered two small high-velocity compact clouds (HVCCs) in HCN $J=4-3$ and $J=3-2$ maps of the central 20 pc of our Galaxy. Both HVCCs have broad velocity widths ($\Delta V \gtrsim 40$ km s$^{-1}$) and compact sizes ($d\sim 1$ pc), and originate from the dense molecular clouds in the position-velocity space. One of them has a faint counterpart in a Paschen-$\alpha$ image. Their spatial structure, kinematics, and absence of luminous stellar object are compatible with the notion that each of the small HVCCs is driven by the plunge of an invisible compact object into a molecular cloud. Such objects are most likely inactive, isolated black holes.
Spectral features from PAH molecules observed in the mid-IR range are typically used to infer the amount of recent and ongoing star formation (SF) on kpc scales around AGN where more traditional methods fail. This assumes that the observed PAH features are excited predominantly by SF. With current ground-based telescopes and the upcoming JWST, much smaller spatial scales can be probed and we aim at testing this assumption in the range of few tens to few hundreds of pc. For that, we spatially map the emitted 11.3{\mu}m PAH surface flux as a function of distance from 0.4-4 arcsec from the centre in 28 nearby AGN using ground-based high-angular resolution mid-IR spectroscopy. We detect and extract the 11.3{\mu}m PAH feature in 13 AGN. The fluxes within each aperture are scaled to a luminosity-normalised distance from the nucleus to be able to compare intrinsic spatial scales of AGN radiation spanning about 2 orders of magnitude in luminosity. For this, we establish an empirical relation between the absorption-corrected X-ray luminosity and the sublimation radius in these sources. Once normalised, the radial profiles of the emitted PAH surface flux show similar radial slopes, with a power-law index of approximately -1.1, and similar absolute values, consistent within a factor of a few of each other as expected from the uncertainty in the intrinsic scale estimate. We interpret this as evidence that the profiles are caused by a common compact central physical process, either the AGN itself or circumnuclear SF linked in strength to the AGN power. A photoionisation-based model of an AGN exciting dense clouds in its environment can reproduce the observed radial slope and confirms that the AGN radiation field is strong enough to explain the observed PAH surface fluxes within ~10-500 pc of the nucleus. Our results advice caution in the use of PAH emission as a SF tracer within a kpc around AGN.
We analyse the poorly-studied open cluster King~1 in the second Galactic quadrant. From wide-field photometry we have studied the spatial distribution of this cluster. We determined that the centre of King~1 is located at $\alpha_{2000}=00^{\rm h}22^{\rm m}$ and $\delta_{2000}=+64\degr23\arcmin$. By parameterizing the stellar density with a King profile we have obtained a central density of $\rho_{0}=6.5\pm0.2$ star arcmin$^{-2}$ and a core radius of $r_{\rm core}=1\farcm9\pm0\farcm2$. By comparing the observed color-magnitude diagram of King~1 with those of similar open clusters and with different sets of isochrones, we have estimated an age of $2.8\pm0.3$ Gyr, a distance modulus of $(m-M)_{\rm o}=10.6\pm0.1$ mag, and a reddening of $E(B-V)=0.80\pm0.05$ mag. To complete our analysis we acquired medium resolution spectra for 189 stars in the area of King~1. From their derived radial velocities we determined an average velocity $\left\langle V_r\right\rangle $=-53.1$\pm$3.1 km s$^{-1}$. From the strength of the infrared \mbox{Ca\,{\sc ii}} lines in red giants we have determined an average metallicity of $\left\langle [M/H]\right\rangle$=+0.07$\pm$0.08 dex. From spectral synthesis we have also estimated an $\alpha$-elements abundance of $\left\langle [\alpha/M]\right\rangle$=-0.10$\pm$0.08 dex.
We have performed Atacama Large Millimeter/submillimeter Array (ALMA) observations in $^{12}$CO($J=2-1$), $^{13}$CO($J=2-1$), C$^{18}$O($J=2-1$), $^{12}$CO($J=3-2$), $^{13}$CO($J=3-2$), and CS($J=7-6$) lines toward the active star-forming region N83C in the Small Magellanic Cloud (SMC), whose metallicity is $\sim$ 1/5 of the Milky Way (MW). The ALMA observations first reveal sub-pc scale molecular structures in $^{12}$CO($J=2-1$) and $^{13}$CO($J=2-1$) emission. We found strong CO peaks associated with young stellar objects (YSOs) identified by the $Spitzer$ Space Telescope, and also found that overall molecular gas is distributed along the edge of the neighboring HII region. We derived a gas density of $\sim 10^4$ cm$^{-3}$ in molecular clouds associated with YSOs based on the virial mass estimated from $^{12}$CO($J=2-1$) emission. This high gas density is presumably due to the effect of the HII region under the low-metallicity (accordingly small-dust content) environment in the SMC; far-UV radiation from the HII region can easily penetrate and photo-dissociate the outer layer of $^{12}$CO molecules in the molecular clouds, and thus only the innermost parts of the molecular clouds are observed even in $^{12}$CO emission. We obtained the CO-to-H$_2$ conversion factor $X_{\rm CO}$ of $\sim 8 \times 10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$ in N83C based on virial masses and CO luminosities, which is four times larger than that in the MW, 2 $\times 10^{20}$ cm$^{-2}$ (K km s$^{-1}$)$^{-1}$. We also discuss the difference in the nature between two high-mass YSOs, each of which is associated with a molecular clump with a mass of about a few $\times 10^3 M_{\odot}$.
We present proper motion measurements of 37 jets and HH objects in the Carina Nebula measured in two epochs of H$\alpha$ images obtained $\sim 10$ yrs apart with HST/ACS. Transverse velocities in all but one jet are faster than $\gtrsim 25$ km s$^{-1}$, confirming that the jet-like H$\alpha$ features identified by Smith et al. (2010) trace outflowing gas. Proper motions constrain the location of the jet-driving source and provide kinematic confirmation of the intermediate-mass protostars that we identify for 20/37 jets. Jet velocities do not correlate with the estimated protostar mass and embedded driving sources do not have slower jets. Instead, transverse velocities (median $\sim 75$ km s$^{-1}$) are similar to those in jets from low-mass stars. Assuming a constant velocity since launch, we compute jet dynamical ages (median $\sim 10^4$ yr). If continuous emission from inner jets traces the duration of the most recent accretion bursts, then these episodes are sustained longer (median $\sim 700$ yr) than the typical decay time of an FU Orionis outburst. These jets can carry appreciable momentum that may be injected into the surrounding environment. The resulting outflow force, $dP/dt$, lies between that measured in low- and high-mass sources, despite the very different observational tracers used. Smooth scaling of the outflow force argues for a common physical process underlying outflows from protostars of all masses. This latest kinematic result adds to a growing body of evidence that intermediate-mass star formation proceeds like a scaled-up version of the formation of low-mass stars.
Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outwards through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud (LMC) is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array (ALMA) are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.
We present elemental abundances for eight unevolved extremely metal-poor stars with $T_{\rm eff}>5500\,\mathrm{K}$, among which seven have $[\mathrm{Fe/H}]<-3.5$. The sample is selected from the Sloan Digital Sky Survey / Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE), and our previous high-resolution spectroscopic follow-up with the Subaru Telescope (Aoki et al.). Several methods to derive stellar parameters are compared, and no significant offset in the derived parameters is found in most cases. From an abundance analysis relative to the standard extremely metal-poor star G 64-12, an average Li abundance for stars with $[\mathrm{Fe/H}]<-3.5$ is $A(\mathrm{Li}) =1.90$, with a standard deviation of $\sigma =0.10$ dex. This result confirms that lower Li abundances are found at lower metallicity, as suggested by previous studies, and demonstrates that the star-to-star scatter is small. The small observed scatter could be a strong constraint on Li-depletion mechanisms proposed for explaining the low Li abundance at lower metallicity. Our analysis for other elements obtained the following results: i) A statistically significant scatter in $[\mathrm{X/Fe}]$ for Na, Mg, Cr, Ti, Sr, and Ba, and an apparent bimodality in $[\mathrm{Na/Fe}]$ with a separation of $\sim 0.8\, \mathrm{dex}$, ii) an absence of a sharp drop in the metallicity distribution, and iii) the existence of a CEMP-$s$ star at $[\mathrm{Fe/H}]\simeq -3.6$ and possibly at $[\mathrm{Fe/H}]\simeq-4.0$, which may provide a constraint on the mixing efficiency of unevolved stars during their main-sequence phase.
I examine a possible spectral distortion of the Cosmic Microwave Background (CMB) due to its absorption by galactic and intergalactic dust. I show that even subtle intergalactic opacity of $1 \times 10^{-7}\, \mathrm{mag}\, h\, \mathrm{Gpc}^{-1}$ at the CMB wavelengths in the local Universe causes non-negligible CMB absorption and decline of the CMB intensity because the opacity steeply increases with redshift. The CMB should be distorted even during the epoch of the Universe defined by redshifts $z < 10$. For this epoch, the maximum spectral distortion of the CMB is at least $20 \times 10^{-22} \,\mathrm{Wm}^{-2}\, \mathrm{Hz}^{-1}\, \mathrm{sr}^{-1}$ at 300 GHz being well above the sensitivity of the COBE/FIRAS, WMAP or Planck flux measurements. If dust mass is considered to be redshift dependent with noticeable dust abundance at redshifts 2-4, the predicted CMB distortion is even higher. The CMB would be distorted also in a perfectly transparent universe due to dust in galaxies but this effect is lower by one order than that due to intergalactic opacity. The fact that the distortion of the CMB by dust is not observed is intriguing and questions either opacity and extinction law measurements or validity of the current model of the Universe.
We study the effect of different feedback prescriptions on the properties of the low redshift ($z\leq1.6$) Ly$\alpha$ forest using a selection of hydrodynamical simulations drawn from the Sherwood simulation suite. The simulations incorporate stellar feedback, AGN feedback and a simplified scheme for efficiently modelling the low column density Ly$\alpha$ forest. We confirm a discrepancy remains between Cosmic Origins Spectrograph (COS) observations of the Ly$\alpha$ forest column density distribution function (CDDF) at $z \simeq 0.1$ for high column density systems ($N_{\rm HI}>10^{14}\rm\,cm^{-2}$), as well as Ly$\alpha$ velocity widths that are too narrow compared to the COS data. Stellar or AGN feedback -- as currently implemented in our simulations -- have only a small effect on the CDDF and velocity width distribution. We conclude that resolving the discrepancy between the COS data and simulations requires an increase in the temperature of overdense gas with $\Delta=4$--$40$, either through additional He$\,\rm \scriptstyle II\ $ photo-heating at $z>2$ or fine-tuned feedback that ejects overdense gas into the IGM at just the right temperature for it to still contribute significantly to the Ly$\alpha$ forest. Alternatively a larger, currently unresolved turbulent component to the line width could resolve the discrepancy.
Weak lensing three-point statistics are powerful probes of the structure of dark matter halos. We propose to use the correlation of the positions of galaxies with the shapes of background galaxy pairs, known as the halo-shear-shear correlation (HSSC), to measure the mean halo ellipticity and the abundance of subhalos in a statistical manner. We run high-resolution cosmological $N$-body simulations and use the outputs to measure the HSSC for galaxy halos and cluster halos. Non-spherical halos cause a characteristic azimuthal variation of the HSSC, and massive subhalos in the outer region near the virial radius contribute to $\sim10\%$ of the HSSC amplitude. We develop an analytic model of the three-point statistics and test its accuracy using the simulation results. We then make forecast for constraining the internal structure of dark matter halos with future galaxy surveys. With 1000 galaxy groups with mass greater than $10^{13.5}\, h^{-1}M_{\odot}$, the average halo ellipticity can be measured with an accuracy of ten percent. A spherical, smooth mass distribution can be ruled out at a $\sim5\sigma$ significance level. The existence of subhalos whose masses are in 1-10 percent of the main halo mass can be detected with $\sim10^4$ galaxies/clusters. We conclude that the HSSC provides valuable information on the structure of dark halos and hence on the nature of dark matter.
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