Astrophysics

An algorithm has been developed for finding the global minimum of a multidimensional error function by fitting model spectral maps into observed ones. Principal component analysis is applied to reduce the dimensionality of the model and the coupling degree between the parameters, and to determine the region of the minimum. The k-nearest neighbors method is used to calculate the optimal parameter values. The algorithm is used to estimate the physical parameters of the contracting dense star-forming core of L1287. Maps in the HCO+(1-0), H13CO+(1-0), HCN(1-0), and H13CN(1-0) lines, calculated within a 1D microturbulent model, are fitted into the observed ones. Estimates are obtained for the physical parameters of the core, including the radial profiles of density ( ??r ??.7 ), turbulent velocity ( ??r ??.4 ), and contraction velocity ( ??r ??.1 ). Confidence intervals are calculated for the parameter values. The power-law index of the contraction-velocity radial profile, considering the determination error, is lower in absolute terms than the expected one in the case of gas collapse onto the protostar in free fall. This result can serve as an argument in favor of a global contraction model for the L1287 core.

The hot halo gas distribution in the inner Milky Way (MW) contains key fossil records of the past energetic feedback processes in the Galactic center. Here we adopt a variety of spherical and disk-like MW halo gas models as initial conditions in a series of simulations to investigate the formation of the Fermi bubbles in the jet-shock scenario. The simulation results are compared directly with relevant X-ray and gamma-ray observations of the Fermi bubbles to constrain the halo gas distribution in the inner Galaxy before the Fermi bubble event. Our best-fit gas density distribution can be described by a power law in radius n e (r)=0.01(r/1~kpc ) ??.5 cm ?? . Our study can not determine if there is an inner density core, which if exists, should be very small with size r c ??.5 kpc. When extrapolating to large radii r??0??0 kpc, our derived density distribution lies appreciably below the recently estimated gas densities from ram-pressure stripping calculations, suggesting that the halo gas density profile either flattens out or has one or more discontinuities within 10?�r??0 kpc. Some of these discontinuities may be related to the eROSITA bubbles, and our derived gas density profile may correspond to the hot gas distribution in the inner eROSITA bubbles about 5 Myr ago.

We report the results of a pilot spectroscopic program of a region at z=5.2 in the GOODS-N field containing an overdensity of galaxies around the well-known submillimeter galaxy HDF850.1. We have selected candidate cluster members from the optical 25 medium-band photometric catalog of the project SHARDS (Survey for High-z Absorption Red and Dead Sources). 17 rest-frame UV selected galaxies (LAEs and LBGs) with 5.15<z_phot<5.27, candidates to be physically associated with the overdensity, have been observed with the instrument OSIRIS at the GranTeCan telescope. 13 out of these 17 (76 per cent) sources have secure spectroscopic confirmations via the Ly α line at the redshift of the galaxy protocluster PCl ??HDF850.1, demonstrating the high reliabilty of our photometric redshift method. 10 out of 13 sources are newly confirmed members. Thus, we increase the number of confirmed members in this overdensity from 13 to 23 objects. In order to fully characterize this structure we combined our dataset with the sample from the literature. Beside the SMG HDF850.1, none of the 23 spectroscopically confirmed members are bright in the far-infrared/submm wavelength regime (SFR_IR< few hundred M_sun yr^-1). The clustering analysis of the whole sample of 23 confirmed members reveals four distinct components in physical space in different evolutionary states, within Delta_z<0.04 from the central region hosting SMG HDF850.1. The halo mass of the whole structure at z=5.2, estimated by a variety of methods, range between 2-8 x 10^12 M_sun. The comparison with literature suggests a large scale assembly comparable to the formation of a central Virgo-like cluster at z=0 with several satellite components which will possibly be incorporated in a single halo if the protocluster is the progenitor of a more massive Coma-like cluster (>10^15 M_sun).

We probe the formation scenarios and the active galactic nuclei (AGN) occupation fraction of ultra-diffuse galaxies (UDGs) in the nearby Coma cluster by utilizing XMM-Newton observations of 779 out of 854 UDG candidates identified by Subaru survey. Their origin is probed by measuring the dark matter halo mass of the stacked sample of UDGs and the population of low-mass X-ray binaries residing in globular clusters. Our measurements suggest that the average UDG population does not have a substantial amount of hot gas or a large number of globular clusters. This supports the formation scenario, in which UDGs are puffed-up dwarf galaxies, agreeing with that obtained for 404 Coma cluster UDGs using Chandra. We also determine AGN occupation fraction of UDGs by cross-correlating the position of UDGs with the detected point sources in Coma. We detect three X-ray sources with detection significance ??? that could be off-centre AGN within 5 arcsec from the centre of the UDG 317, UDG 432, and UDG 535. We identify an optical counterpart for the X-ray source associated with the UDG 317, suggesting that this source is more likely an off-centre AGN. Based on the current data, however, we cannot conclusively constrain whether the detected AGN is residing in the Coma cluster or not.

We present deep (250 ks) Chandra observations of the nearby galaxy group NGC 1600, which has at its centre an ultramassive black hole (17 ± 1.5 billion M ??). The exceptionally large mass of the black hole coupled with its low redshift makes it one of only a handful of black holes for which spatially resolved temperature and density profiles can be obtained within the Bondi radius with the high spatial resolution of Chandra. We analyzed the hot gas properties within the Bondi accretion radius R B =1.2" - 1.7"= 0.38 - 0.54 kpc. Within a ?? kpc radius, we find two temperature components with statistical significance. Both the single temperature and two temperature models show only a very slight rise in temperature towards the centre, and are consistent with being flat. This is in contrast with the expectation from Bondi accretion for a temperature profile which increases towards the centre, and appears to indicate that the dynamics of the gas are not being determined by the central black hole. The density profile follows a relatively shallow ??? r ?�[0.61±0.13] relationship within the Bondi radius, which suggests that the true accretion rate on to the black hole may be lower than the classical Bondi accretion rate.

The polarization properties of radio sources powered by an Active Galactic Nucleus (AGN) have attracted considerable attention because of the significance of magnetic fields in the physics of these sources, their use as probes of plasma along the line of sight, and as a possible contaminant of polarization measurements of the cosmic microwave background. For each of these applications, a better understanding of the statistics of polarization in relation to source characteristics is crucial. In this paper, we derive the median fractional polarization, ? 0,med , of large samples of radio sources with 1.4 GHz flux density 6.6< S 1.4 <70 mJy, by stacking 1.4 GHz NVSS polarized intensity as a function of angular size derived from the FIRST survey. Five samples with deconvolved mean angular size 1.8" to 8.2" and two samples of symmetric double sources are analyzed. These samples represent most sources smaller than or near the median angular size of the mJy radio source population We find that the median fractional polarization ? 0,med at 1.4 GHz is a strong function of source angular size less than ~5" and a weak function of angular size for larger sources up to ~8". We interpret our results as depolarization inside the AGN host galaxy and its circumgalactic medium. The curvature of the low-frequency radio spectrum is found to anti-correlate with ? 0,med , a further sign that depolarization is related to the source.

The dominant site of production of r -process elements remains unclear despite recent observations of a neutron star merger. Observational constraints on the properties of the sites can be obtained by comparing r -process abundances in different environments. The recent Gaia data releases and large samples from high-resolution optical spectroscopic surveys are enabling us to compare r -process element abundances between stars formed in an accreted dwarf galaxy, Gaia-Enceladus, and those formed in the Milky Way. We aim to understand the origin of r -process elements in Gaia-Enceladus. We first construct a sample of stars to study Eu abundances without being affected by the detection limit. We then kinematically select 71 Gaia-Enceladus stars and 93 in-situ stars from the Galactic Archaeology with HERMES (GALAH) DR3, of which 50 and 75 stars can be used to study Eu reliably. Gaia-Enceladus stars clearly show higher ratios of [{Eu}/{Mg}] than in-situ stars. High [{Eu}/{Mg}] along with low [{Mg}/{Fe}] are also seen in relatively massive satellite galaxies such as the LMC, Fornax, and Sagittarius dwarfs. On the other hand, unlike these galaxies, Gaia-Enceladus does not show enhanced [{Ba}/{Eu}] or [{La}/{Eu}] ratios suggesting a lack of significant s -process contribution. From comparisons with simple chemical evolution models, we show that the high [{Eu}/{Mg}] of Gaia-Enceladus can naturally be explained by considering r -process enrichment by neutron-star mergers with delay time distribution that follows a similar power-law as type~Ia supernovae but with a shorter minimum delay time.

We report the 888 MHz radio detection in the Rapid ASKAP Continuum Survey (RACS) of VIK J2318 ??3113, a z =6.44 quasar. Its radio luminosity (1.2 ? 10 26 W Hz ?? at 5 GHz) compared to the optical luminosity (1.8 ? 10 24 W Hz ?? at 4400 A) makes it the most distant radio-loud quasar observed so far, with a radio loudness R ??70 (R = L 5GHz / L 4400A ). Moreover, the high bolometric luminosity of the source (L bol =7.4 ? 10 46 erg s ?? ) suggests the presence of a supermassive black hole with a high mass ( ??6 ? 10 8 M ??) at a time when the Universe was younger than a billion years. Combining the new radio data from RACS with previous ASKAP observations at the same frequency, we found that the flux density of the source may have varied by a factor of ??2, which could suggest the presence of a relativistic jet oriented towards the line of sight, that is, a blazar nature. However, currently available radio data do not allow us to firmly characterise the orientation of the source. Further radio and X-ray observations are needed.

We present the results of our multifrequency observations for 10 ultraluminous infrared galaxies (ULIRGs) made by the Karl G. Jansky Very Large Array at 1.4, 5.5, 9.0, and 14.0 GHz. Our sample is selected from ULIRGs whose active galactic nuclei (AGNs) are not found at optical wavelengths ( ??70% of the entire ULIRGs), but whose presence is suggested by mid-infrared or submillimetre observations ( >50 % of the non-AGN ULIRGs at optical wavelengths). The statistical properties of the targets are similar to those of the entire ULIRG sample, which implies that ULIRGs have common radiative processes regardless of the presence of optical AGNs, and thus AGNs might equally contribute to the radio emission of every ULIRG. Although their spectra are mainly explained by starbursts and/or merger activity, some individual sources suggest contributions from AGNs. IRAS 00188 ??0856, whose optical morphology is not disturbed, shows a large nonthermal fraction and a spectral break at high frequency, which can be explained by synchrotron ageing of nonthermal plasma emitted from AGNs. In addition, we find 100-kpc scale extended emission associated with IRAS 01004 ??2237. The two-sided morphology and absence of extended X-ray emission suggest that this system is not induced by a merger in a cluster but originates from AGN activity.

The H2 molecule has two nuclear spin isomers, the so-called ortho and para isomers. Nuclear spin conversion (NSC) between these states is forbidden in the gas phase. The energy difference between the lowest ortho and para states is as large as 14.7 meV, corresponding to ~170 K. Therefore, each state of H2 differently affects not only the chemistry but also the macroscopic gas dynamics in space, and thus, the ortho-to-para abundance ratio (OPR) of H2 has significant impacts on various astronomical phenomena. For a long time, the OPR of nascent H2 upon formation on dust grains has been assumed to have a statistical value of three and to gradually equilibrate in the gas phase at the temperature of the circumstances. Recently, NSC of H2 was experimentally revealed to occur on water ice at very low temperatures and thus incorporated into gas-dust chemical models. However, H2 molecules should form well before dust grains are coated by water ice. Information about how the OPR of H2 behaves on bare silicate dust before ice-mantle formation is lacking. Knowing the influence of the OPR of H2 if the OPR changes even on a bare silicate surface within an astronomically meaningful time scale is desirable. We report the first laboratory measurements of NSC of H2 physisorbed on amorphous silicate (Mg2SiO4) at temperatures up to 18 K. The conversion was found to occur very rapidly.