We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 \(\text{H}\thinspace \text{II}\) regions and ring nebulae surrounding massive O stars. We ...revise the Galactocentric distances of the objects considering {\it Gaia} DR2 parallaxes and determine the physical conditions and the ionic abundance of He\(^{+}\) in a homogeneous way, using between 3 and 10 \(\text{He}\thinspace \text{I}\) recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ICF(He) schemes. The slope of the gradient is always negative and weakly dependent on the ICF(He) scheme, especially when only the objects with log(\(\eta\)) \(<\) 0.9 are considered. The slope values go from \(-\)0.0078 to \(-\)0.0044 dex kpc\(^{-1}\), consistent with the predictions of chemical evolution models of the Milky Way and chemodynamical simulations of disc galaxies. Finally, we estimate the abundance deviations of He, O and N in a sample of ring nebulae around Galactic WR stars, finding a quite similar He overabundance of about +0.24 \(\pm\) 0.11 dex in three stellar ejecta ring nebulae.
We present the analysis of physical conditions, chemical composition and kinematic properties of two bow shocks -HH529 II and HH529 III- of the fully photoionized Herbig-Haro object HH 529 in the ...Orion Nebula. The data were obtained with the Ultraviolet and Visual Echelle Spectrograph at the 8.2m Very Large Telescope and 20 years of Hubble Space Telescope imaging. We separate the emission of the high-velocity components of HH529 II and III from the nebular one, determining \(n_{\rm e}\) and \(T_{\rm e}\) in all components through multiple diagnostics, including some based on recombination lines (RLs). We derive ionic abundances of several ions, based on collisionally excited lines (CELs) and RLs. We find a good agreement between the predictions of the temperature fluctuation paradigm (\(t^2\)) and the abundance discrepancy factor (ADF) in the main emission of the Orion Nebula. However, \(t^2\) can not account for the higher ADF found in HH 529 II and III. We estimate a 6% of Fe in the gas-phase of the Orion Nebula, while this value increases to 14% in HH 529 II and between 10% and 25% in HH 529 III. We find that such increase is probably due to the destruction of dust grains in the bow shocks. We find an overabundance of C, O, Ne, S, Cl and Ar of about 0.1 dex in HH 529 II-III that might be related to the inclusion of H-deficient material from the source of the HH 529 flow. We determine the proper motions of HH 529 finding multiple discrete features. We estimate a flow angle with respect to the sky plane of \(58\pm 4^{\circ}\) for HH 529.
We study the sensitivity of the methods available for abundance determinations in H II regions to potential observational problems. We compare the dispersions they introduce around the oxygen and ...nitrogen abundance gradients when applied to five different sets of spectra of H II regions in the galaxy M81. Our sample contains 116 H II regions with galactocentric distances of 3 to 33 kpc, including 48 regions observed by us with the OSIRIS long-slit spectrograph at the 10.4-m Gran Telescopio Canarias telescope. The direct method can be applied to 31 regions, where we can get estimates of the electron temperature. The different methods imply oxygen abundance gradients with slopes of -0.010 to -0.002 dex kpc-1, and dispersions in the range 0.06-0.25 dex. The direct method produces the shallowest slope and the largest dispersion, illustrating the difficulty of obtaining good estimates of the electron temperature. Three of the strong-line methods, C, ONS, and N2, are remarkably robust, with dispersions of ~ 0.06 dex, and slopes in the range -0.008 to -0.006 dex kpc-1. The robustness of each method can be directly related to its sensitivity to the line intensity ratios that are more difficult to measure properly. Since the results of the N2 method depend strongly on the N/O abundance ratio and on the ionization parameter, we recommend the use of the C and ONS methods when no temperature estimates are available or when they have poor quality, although the behaviour of these methods when confronted with regions that have different properties and different values of N/O should be explored.
We present an analysis of the ultraviolet (UV) continuum slopes (\(\beta\)) for a sample of \(172\) galaxy candidates at \(8 < z_{\mathrm{phot}} < 16\) selected from a combination of JWST NIRCam ...imaging and COSMOS/UltraVISTA ground-based near-infrared imaging. Focusing primarily on a new sample of \(121\) galaxies at \(\langle z \rangle \simeq 11\) selected from \(\simeq 320\) arcmin\(^2\) of public JWST imaging data across \(15\) independent data sets, we investigate the evolution of \(\beta\) in the galaxy population at \(z \geq 9\). We find a significant trend between \(\beta\) and redshift, with the inverse-variance weighted mean UV slope evolving from \(\langle \beta \rangle = -2.17 \pm 0.06\) at \(z = 9.5\) to \(\langle \beta \rangle = -2.59 \pm 0.06\) at \(z = 11.5\). Based on a comparison with stellar population models including nebular continuum emission, we find that at \(z>10.5\) the average UV continuum slope is consistent with the intrinsic blue limit of dust-free stellar populations \((\beta_{\mathrm{int}} \simeq -2.6)\). These results suggest that the moderately dust-reddened galaxy population at \(z < 10\) was essentially unattenuated at \(z \simeq 11\). The extremely blue galaxies being uncovered at \(z>10\) place important constraints on dust attenuation in galaxies in the early Universe, and imply that the already observed galaxy population is likely supplying an ionising photon budget capable of maintaining ionised IGM fractions of \(\gtrsim 5\) per cent at \(z\simeq11\).
We present a new determination of the evolving galaxy UV luminosity function
(LF) over the redshift range $8.5<z<15.5$ using a combination of several major
Cycle-1 JWST imaging programmes - PRIMER, ...JADES and NGDEEP. This multi-field
approach yields a total of $\simeq370$ sq. arcmin of JWST/NIRCam imaging,
reaching (5-$\sigma$) depths of $\simeq30$ AB mag in the deepest regions. We
select a sample of 2548 galaxies with a significant probability of lying at
high redshift ($p(z>8.5)>0.05$) to undertake a statistical calculation of the
UV LF. Our new measurements span $\simeq4$ magnitudes in UV luminosity at
$z=9-12.5$, placing new constraints on both the shape and evolution of the LF
at early times. Our measurements yield a new estimate of the early evolution of
cosmic star-formation rate density ($\rho_{\rm{SFR}}$) confirming the gradual
decline deduced from early JWST studies, at least out to $z \simeq 12$. Finally
we show that the observed early evolution of the galaxy UV LF (and
$\rho_{\rm{SFR}}$) can be reproduced in a ${\rm \Lambda}$CDM Universe, with no
change in dust properties or star-formation efficiency required out to $z
\simeq 12$. Instead, a progressive trend towards younger stellar population
ages can reproduce the observations, and the typical ages required at $z
\simeq$ 8, 9, 10, and 11 all converge on $\simeq 380-330$ Myr after the Big
Bang, indicative of a rapid emergence of early galaxies at $z \simeq 12 - 13$.
This is consistent with the first indications of a steeper drop-off in
$\rho_{\rm{SFR}}$ we find beyond $z \simeq 13$, possibly reflecting the rapid
evolution of the halo mass function at earlier times.
One of the surprising early findings with JWST has been the discovery of a
strong "roll-over" or a softening of the absorption edge of Ly$\alpha$ in a
large number of galaxies at ($z\gtrsim 6$), in ...addition to systematic offsets
from photometric redshift estimates and fundamental galaxy scaling relations.
This has been interpreted as damped Ly$\alpha$ absorption (DLA) wings from high
column densities of neutral atomic hydrogen (HI), signifying major gas
accretion events in the formation of these galaxies. To explore this new
phenomenon systematically, we assemble the JWST/NIRSpec PRImordial gas Mass
AssembLy (PRIMAL) legacy survey of 494 galaxies at $z=5.5-13.4$. We
characterize this benchmark sample in full and spectroscopically derive the
galaxy redshifts, metallicities, star-formation rates, and ultraviolet slopes.
We define a new diagnostic, the Ly$\alpha$ damping parameter $D_{\rm Ly\alpha}$
to measure and quantify the Ly$\alpha$ emission strength, HI fraction in the
IGM, or local HI column density for each source. The JWST-PRIMAL survey is
based on the spectroscopic DAWN JWST Archive (DJA-Spec). All the software,
reduced spectra, and spectroscopically derived quantities and catalogs are made
publicly available in dedicated repositories. The fraction of strong galaxy
DLAs are found to be in the range $65-95\%$ at $z>5.5$. The fraction of strong
Ly$\alpha$ emitters (LAEs) is found to increase with decreasing redshift, in
qualitative agreement with previous observational results, and are
predominantly associated with low-metallicity and UV faint galaxies. By
contrast, strong DLAs are observed in galaxies with a variety of intrinsic
physical properties. Our results indicate that strong DLAs likely reflect a
particular early assembly phase of reionization-era galaxies, at which point
they are largely dominated by pristine HI gas accretion. abridged
The quest for quiet or dormant black holes has been ongoing since several decades. Ellipsoidal variables possibly indicate the existence of a very high-mass invisible companion and are thought to be ...one of the best ways to find such dormant black holes. This, however, is not a panacea as we show here with one example. We indeed report the discovery of a new semi-detached interacting binary, V1315 Cas, discovered as an ellipsoidal variable. Using data from photometric surveys (ASAS-SN, TESS) and high-resolution spectroscopy, we derived a nearly circular orbit with an orbital period of \(P_{\rm{orb}}\)=34.54 d. The binary system consists of an evolved F-type star primary that is likely still filling its Roche lobe and a B-type star secondary. Using \textsc{phoebe}2, we derived the following masses and radii: for the primary, \(M_p =0.84 \pm 0.03 \, M_\odot\) and \(R_p =18.51^{+0.12}_{-0.07} \, R_\odot\); for the secondary, \(M_s =7.3 \pm 0.3 \,M_\odot\) and \(R_s =4.02^{+2.3}_{-2.0}\,R_\odot\). Modeling the evolution of the system with MESA, we found an age of \(\sim\)7.7e7 years. The system is at the end of a period of rapid non-conservative mass transfer that reversed its mass ratio, while significantly widening its orbit. The primary shows carbon depletion and nitrogen overabundance, indicative of CNO processed material being exposed due to mass transfer. An infrared excess as well as stationary H\(\alpha\) emission suggest the presence of a circumstellar or circumbinary disc. V1315 Cas will likely become a detached stripped star binary.
We obtained new quantitative determinations of the nitrogen abundance and a consistent relation between nitrogen and oxygen abundances for a sample of Seyfert 2 galaxies located at redshift \(z < ...0.1\). We carried out this analysis using the Cloudy code to build detailed photoionization models. We were able to reproduce observed optical narrow emission line intensities for 44 sources compiled from the literature. Our results show that Seyfert 2 nuclei have nitrogen abundances ranging from \(\sim0.3\) to \(\sim 7.5\) times the solar value. We derived the relation \(\rm \log(N/H)=1.05 (\pm0.09) \times \log(O/H) -0.35 (\pm 0.33\)). Results for N/O vs. O/H abundance ratios derived for Seyfert 2 galaxies are in consonance with those recently derived for a sample of extragalactic disk HII regions with high metallicity.
We present a new determination of the evolving galaxy UV luminosity function (LF) over the redshift range \(8.5<z<15.5\) using a combination of several major Cycle-1 JWST imaging programmes - PRIMER, ...JADES and NGDEEP. This multi-field approach yields a total of \(\simeq370\) sq. arcmin of JWST/NIRCam imaging, reaching (5-\(\sigma\)) depths of \(\simeq30\) AB mag in the deepest regions. We select a sample of 2548 galaxies with a significant probability of lying at high redshift (\(p(z>8.5)>0.05\)) to undertake a statistical calculation of the UV LF. Our new measurements span \(\simeq4\) magnitudes in UV luminosity at \(z=9-12.5\), placing new constraints on both the shape and evolution of the LF at early times. Our measurements yield a new estimate of the early evolution of cosmic star-formation rate density (\(\rho_{\rm{SFR}}\)) confirming the gradual decline deduced from early JWST studies, at least out to \(z \simeq 12\). Finally we show that the observed early evolution of the galaxy UV LF (and \(\rho_{\rm{SFR}}\)) can be reproduced in a \({\rm \Lambda}\)CDM Universe, with no change in dust properties or star-formation efficiency required out to \(z \simeq 12\). Instead, a progressive trend towards younger stellar population ages can reproduce the observations, and the typical ages required at \(z \simeq\) 8, 9, 10, and 11 all converge on \(\simeq 380-330\) Myr after the Big Bang, indicative of a rapid emergence of early galaxies at \(z \simeq 12 - 13\). This is consistent with the first indications of a steeper drop-off in \(\rho_{\rm{SFR}}\) we find beyond \(z \simeq 13\), possibly reflecting the rapid evolution of the halo mass function at earlier times.
One of the surprising early findings with JWST has been the discovery of a strong "roll-over" or a softening of the absorption edge of Ly\(\alpha\) in a large number of galaxies at (\(z\gtrsim 6\)), ...in addition to systematic offsets from photometric redshift estimates and fundamental galaxy scaling relations. This has been interpreted as damped Ly\(\alpha\) absorption (DLA) wings from high column densities of neutral atomic hydrogen (HI), signifying major gas accretion events in the formation of these galaxies. To explore this new phenomenon systematically, we assemble the JWST/NIRSpec PRImordial gas Mass AssembLy (PRIMAL) legacy survey of 494 galaxies at \(z=5.5-13.4\). We characterize this benchmark sample in full and spectroscopically derive the galaxy redshifts, metallicities, star-formation rates, and ultraviolet slopes. We define a new diagnostic, the Ly\(\alpha\) damping parameter \(D_{\rm Ly\alpha}\) to measure and quantify the Ly\(\alpha\) emission strength, HI fraction in the IGM, or local HI column density for each source. The JWST-PRIMAL survey is based on the spectroscopic DAWN JWST Archive (DJA-Spec). All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. The fraction of strong galaxy DLAs are found to be in the range \(65-95\%\) at \(z>5.5\). The fraction of strong Ly\(\alpha\) emitters (LAEs) is found to increase with decreasing redshift, in qualitative agreement with previous observational results, and are predominantly associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine HI gas accretion. abridged
