Ciencias Naturales
Permanent URI for this community
Browse
Browsing Ciencias Naturales by Author "[et al.]"
ABYSS. I. Targeting Strategy for the APOGEE and BOSS Young Star Survey in SDSS-V
(ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 2023-05-01) Kounkel, M; Zari, E; Covey, K; Tkachenko, A; [et al.]
The fifth iteration of the Sloan Digital Sky Survey is set to obtain optical and near-infrared spectra of similar to 5 million stars of all ages and masses throughout the Milky Way. As a part of these efforts, APOGEE and BOSS Young Star Survey (ABYSS) will observe similar to 10(5) stars with ages <30 Myr that have been selected using a set of homogeneous selection functions that make use of different tracers of youth. The ABYSS targeting strategy we describe in this paper is aimed to provide the largest spectroscopic census of young stars to date. It consists of eight different types of selection criteria that take the position on the H-R diagram, infrared excess, variability, as well as the position in phase space in consideration. The resulting catalog of similar to 200,000 sources (of which a half are expected to be observed) provides representative coverage of the young Galaxy, including both nearby diffuse associations as well as more distant massive complexes, reaching toward the inner Galaxy and the Galactic center.
CLASSY VII Lyα Profiles: The Structure and Kinematics of Neutral Gas and Implications for LyC Escape in Reionization-era Analogs
(ASTROPHYSICAL JOURNAL, 2023-10-01) Hu, WD; Martin, CL; Gronke, M; Gazagnes, S; Hayes, M; Chisholm, J; Heckman, T; Mingozzi, M; [et al.]
Ly alpha line profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Ly alpha line profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Ly alpha emission profile in the bottom of a damped, Ly alpha absorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Ly alpha absorption and the Ly alpha emission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Ly alpha exchange between high-N-H I and low-N-H I paths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Ly alpha peak separation and the [O III]/[O II] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Ly alpha peak separation decreases. We combine measurements of Ly alpha peak separation and Ly alpha red peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Ly alpha trough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Ly alpha peak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Ly alpha photons outside the spectroscopic aperture reshapes Ly alpha profiles because the distances to these compact starbursts span a large range.
HST proper motions on the far side of the Galactic bar-data
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-07-04) Soto, M; Kuijken, K; Rich, RM; Clarkson, WI; [et al.]
This is the third paper in a series that attempts to observe a clear signature of the Galactic bar/bulge using kinematic observations of the bulge stellar populations in low foreground extinction windows. We report on the detection of & SIM;100 000 new proper motions in four fields covering the far side of the Galactic bar/bulge, at negative longitudes. Our proper motions have been obtained using observations from the Advance Camera for Surveys (ACS), on board of the Hubble Space Telescope (HST), with a time-baseline of 8-9 years, which has produced accuracies better than 0.5 mas yr(-1) for a significant fraction of the stellar populations with F814W < 23 mag. Interestingly, as shown in previous works, the Hess diagrams show a strikingly similar proper motion distribution to fields closer to the Galactic center and consistent with an old stellar population. The observed kinematics point to a significant bulge rotation, which seems to predominate even in fields as far as l & SIME; -8 & DEG;, and is also reflected in the changes of the velocity ellipsoid in the l, b plane as a function of distance.
Insights into the reionization epoch from cosmic-noon-C IV emitters in the VANDELS survey
(ASTRONOMY & ASTROPHYSICS, 2023-06-27) Mascia, S; Pentericci, L; Saxena, A; Belfiori, D; [et al.]
Recently, intense emission from nebular C III] and C IV emission lines have been observed in galaxies in the epoch of reionization (z > 6) and have been proposed as the prime way of measuring their redshift and studying their stellar populations. These galaxies might represent the best examples of cosmic reionizers, as suggested by recent low-z observations of Lyman continuum emitting galaxies, but it is hard to directly study the production and escape of ionizing photons at such high redshifts. The ESO spectroscopic public survey VANDELS offers the unique opportunity to find rare examples of such galaxies at cosmic noon (z & SIM; 3), thanks to the ultra deep observations available. We have selected a sample of 39 galaxies showing C IV emission, whose origin (after a careful comparison to photoionization models) can be ascribed to star formation and not to active galactic nuclei. By using a multiwavelength approach, we determined their physical properties including metallicity and the ionization parameter and compared them to the properties of the parent population to understand what the ingredients are that could characterize the analogs of the cosmic reionizers. We find that C IV emitters are galaxies with high photon production efficiency and there are strong indications that they might also have a large escape fraction: given the visibility of C IV in the epoch of reionization, this could become the best tool to pinpoint the cosmic reioinzers.
Light elements Na and Al in 58 bulge spheroid stars from APOGEE
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-09-29) Barbuy, B; Friaça, ACS; Ernandes, H; Moura, T; Masseron, T; Cunha, K; Smith, VV; Souto, D; Pérez-Villegas, A; Souza, SO; Chiappini, C; Queiroz, ABA; Fernández-Trincado, JG; [et al.]
We identified a sample of 58 candidate stars with metallicity [Fe/H]less than or similar to-0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20percent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H]less than or similar to-1.0. For the lower-metallicity end ([Fe/H<-2.5), hypernovae are assumed to be the main contributor to yields.
Origins of the Evil Eye: M64's Stellar Halo Reveals the Recent Accretion of an SMC-mass Satellite
(ASTROPHYSICAL JOURNAL LETTERS, 2023-06-01) Smercina, A; Bell, EF; Price, PA; Bailin, J; [et al.]
M64, often called the Evil Eye galaxy, is unique among local galaxies. Beyond its dramatic, dusty nucleus, it also hosts an outer gas disk that counter-rotates relative to its stars. The mass of this outer disk is comparable to the gas content of the Small Magellanic Cloud (SMC), prompting the idea that it was likely accreted in a recent minor merger. Yet, detailed follow-up studies of M64's outer disk have shown no evidence of such an event, leading to other interpretations, such as a flyby interaction with the distant diffuse satellite Coma P. We present Subaru Hyper Suprime-Cam observations of M64's stellar halo, which resolve its stellar populations and reveal a spectacular radial shell feature, oriented similar to 30 degrees relative to the major axis and along the rotation axis of the outer gas disk. The shell is similar to 45 kpc southeast of M64, while a similar but more diffuse plume to the northwest extends to >100 kpc. We estimate a stellar mass and metallicity for the southern shell of M-star = 1.80 +/- 0.54 x 10(8) M-circle dot and [M/H] = -1.0, respectively, and a similar mass of 1.42 +/- 0.71 x 10(8) M-circle dot for the northern plume. Taking into account the accreted material in M64's inner disk, we estimate a total stellar mass for the progenitor satellite of M-star,M-prog similar or equal to 5 x 10(8) M-circle dot. These results suggest that M64 is in the final stages of a minor merger with a gas-rich satellite strikingly similar to the SMC, in which M64's accreted counter-rotating gas originated, and which is responsible for the formation of its dusty inner star-forming disk.
Pre-main-sequence Brackett Emitters in the APOGEE DR17 Catalog: Line Strengths and Physical Properties of Accretion Columns
(ASTROPHYSICAL JOURNAL, 2023-02-01) Campbell, H; Khilfeh, E; Covey, KR; Kounkel, M; [et al.]
Very young (t less than or similar to 10 Myr) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar disks to the surface of the star. Upon impacting the stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br) 11-20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main-sequence accretors. For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities of n ( e ) = 10(11)-10(12) cm(-3), and excitation temperatures that are inversely correlated with electron density (from T similar to 5000 K for n ( e ) similar to 10(12) cm(-3) to T similar to 12,500 K at n ( e ) similar to 10(11) cm(-3)). These physical parameters are in good agreement with predictions from modeling of accretion streams that account for the hydrodynamics and radiative transfer within the accretion stream. We also present a supplementary catalog of line measurements from 9733 spectra of 4255 Brackett emission-line sources in the APOGEE Data Release 17 data set.
Stellar Properties for a Comprehensive Collection of Star-forming Regions in the SDSS APOGEE-2 Survey
(ASTRONOMICAL JOURNAL, 2023-01-01) Román-Zúñiga, CG; Kounkel, M; Hernández, J; Ramírez, KP; [et al.]
The Sloan Digital Sky Survey IV APOGEE-2 primary science goal was to observe red giant stars throughout the Galaxy to study its dynamics, morphology, and chemical evolution. The APOGEE instrument, a high-resolution 300fiber H-band (1.55-1.71 mu m) spectrograph, is also ideal to study other stellar populations in the Galaxy, among which are a number of star-forming regions and young open clusters. We present the results of the determination of six stellar properties (Teff, log g, [Fe/H], L/L-circle dot, M/M-circle dot, and age) for a sample that is composed of 3360 young stars, of subsolar to supersolar types, in 16 Galactic star formation and young open cluster regions. Those sources were selected by using a clustering method that removes most of the field contamination. Samples were also refined by removing targets affected by various systematic effects of the parameter determination. The final samples are presented in a comprehensive catalog that includes all six estimated parameters. This overview study also includes parameter spatial distribution maps for all regions and Hertzsprung-Russell (log L/L-circle dot vs. T-eff) diagrams. This study serves as a guide for detailed studies on individual regions and paves the way for the future studies on the global properties of stars in the pre-main-sequence phase of stellar evolution using more robust samples.
Structure, Kinematics, and Observability of the Large Magellanic Cloud's Dynamical Friction Wake in Cold versus Fuzzy Dark Matter
(ASTROPHYSICAL JOURNAL, 2023-09-01) Foote, HR; Besla, G; Mocz, P; Garavito-Camargo, N; [et al.]
The Large Magellanic Cloud (LMC) will induce a dynamical friction (DF) wake on infall to the Milky Way (MW). The MW's stellar halo will respond to the gravity of the LMC and the dark matter (DM) wake, forming a stellar counterpart to the DM wake. This provides a novel opportunity to constrain the properties of the DM particle. We present a suite of high-resolution, windtunnel-style simulations of the LMC's DF wake that compare the structure, kinematics, and stellar tracer response of the DM wake in cold DM (CDM), with and without self-gravity, versus fuzzy DM (FDM) with m a = 10-23 eV. We conclude that the self-gravity of the DM wake cannot be ignored. Its inclusion raises the wake's density by & SIM;10%, and holds the wake together over larger distances (& SIM;50 kpc) than if self-gravity is ignored. The DM wake's mass is comparable to the LMC's infall mass, meaning the DM wake is a significant perturber to the dynamics of MW halo tracers. An FDM wake is more granular in structure and is & SIM;20% dynamically colder than a CDM wake, but with comparable density. The granularity of an FDM wake increases the stars' kinematic response at the percent level compared to CDM, providing a possible avenue of distinguishing a CDM versus FDM wake. This underscores the need for kinematic measurements of stars in the stellar halo at distances of 70-100 kpc.
Taking a break: Paused accretion in the symbiotic binary RT Cru
(ASTRONOMY & ASTROPHYSICS, 2023-01-02) Pujol, A; Luna, GJM; Mukai, K; Sokoloski, JL; [et al.]
Symbiotic binaries sometimes hide their symbiotic nature for significant periods of time. There is mounting observational evidence that, in symbiotics that are powered solely by the accretion of the red giant's wind material onto a white dwarf, without any quasisteady shell burning on the surface of the white dwarf, the characteristic emission lines in the optical spectrum can vanish, leaving the semblance of an isolated red giant spectrum. Here we present compelling evidence that this disappearance of optical emission lines from the spectrum of RT Cru in 2019 was due to a decrease in the accretion rate, which we derived by modeling the X-ray spectrum. This drop in accretion rate leads to a lower flux of ionizing photons and thus to faint or absent photoionization emission lines in the optical spectrum. We observed the white dwarf symbiotic RT Cru with XMM-Newton and Swift in X-rays and UV and collected ground-based optical spectra and photometry obtained over the last 33 yr. This long-term coverage shows that, during most of the year 2019, the accretion rate onto the white dwarf was so low,. M = (3 :2 +/- 0 :06) x 10(-1)1 M fi yr(-1) (d /2.52 kpc)(2), that the historically detected hard X-ray emission almost vanished, the UV flux faded by roughly 5 mag, the U, B, and V flickering amplitude decreased, and the Balmer lines virtually disappeared from 2019 January through March. Long-lasting low-accretion episodes such as the one reported here may hamper the chances of RT Cru experiencing a nova-type outburst despite the high mass of the accreting white dwarf.
The impact of the Large Magellanic Cloud on dark matter direct detection signals
(JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 2023-10-27) Smith-Orlik, A; Ronaghi, N; Bozorgnia, N; Cautun, M; [et al.]
We study the effect of the Large Magellanic Cloud (LMC) on the dark matter (DM) distribution in the Solar neighborhood, utilizing the Auriga magneto-hydrodynamical simulations of Milky Way (MW) analogues that have an LMC-like system. We extract the local DM velocity distribution at different times during the orbit of the LMC around the MW in the simulations. As found in previous idealized simulations of the MW-LMC system, we find that the DM particles in the Solar neighborhood originating from the LMC analogue dominate the high speed tail of the local DM speed distribution. Furthermore, the native DM particles of the MW in the Solar region are boosted to higher speeds as a result of a response to the LMC's motion. We simulate the signals expected in near future xenon, germanium, and silicon direct detection experiments, considering DM interactions with target nuclei or electrons. We find that the presence of the LMC causes a considerable shift in the expected direct detection exclusion limits towards smaller cross sections and DM masses, with the effect being more prominent for low mass DM. Hence, our study shows, for the first time, that the LMC's influence on the local DM distribution is significant even in fully cosmological MW analogues.
The Low-redshift Lyman Continuum Survey: Optically Thin and Thick Mg ii Lines as Probes of Lyman Continuum Escape
(ASTROPHYSICAL JOURNAL, 2023-01-01) Xu, XF; Henry, A; Heckman, T; Chisholm, J; [et al.]
The Mg ii lambda lambda 2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Ly alpha and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg ii or strong LyC emission. Here, we present the first study of Mg ii to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg ii, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg ii profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of similar to 2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg ii emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg ii. We then find that Mg ii strongly correlates with Ly alpha in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg ii profiles. Furthermore, we show that, for galaxies that are categorized as Mg ii emitters, one can use the information of Mg ii, metallicity, and dust to estimate the escape fraction of LyC within a factor of similar to 3. These findings confirm that Mg ii lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Ly alpha and LyC.
The stellar halo in Local Group Hestia simulations
(ASTRONOMY & ASTROPHYSICS, 2023-09-11) Khoperskov, S; Minchev, I; Libeskind, N; Belokurov, V; [et al.]
Stellar chemical abundances and kinematics provide key information for recovering the assembly history of galaxies. In this work we explore the chemo-chrono-kinematics of accreted and in situ stellar populations, by analyzing six M31 /Milky Way (MW) analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We show that elemental abundances ([Fe =H], [Mg =Fe]) of merger debris in the stellar haloes are chemically distinct from the survived dwarf galaxies, in that they are [ alpha/Fe]-enhanced and have lower metallicity in the same stellar mass range. Therefore, mergers debris have abundances expected for stars originating from dwarfs that had their star formation activity quenched at early times. Accreted stellar haloes, including individual debris, reveal [Fe=H] and [Mg=Fe] gradients in the E - L-z plane, with the most metal-rich, [alpha/Fe]-poor stars, which have formed in the inner parts of the disrupted systems before the merger, contributing mainly to the central regions of the host galaxies. This results in negative metallicity gradients in the accreted components of stellar haloes at z = 0, seen also for the individual merger debris. We suggest, therefore, that abundance measurements of halo stars in the inner MW will allow constraining better the parameters, such as the mass and merger time, of MW ' s most massive merger Gaia-Sausage-Enceladus. The metallicity distribution functions (MDFs) of the individual debris show several peaks and the majority of debris have lower metallicity than the in situ stars in the prograde part of the E-L-z space. At the same time, non-rotating and retrograde accreted populations are very similar to the in situ stars in terms of [Fe=H] abundance. Prograde accreted stars show a prominent knee in the [Fe=H]-[Mg=Fe] plane, reaching up to solar [Mg=Fe], while retrograde stars typically contribute to the high-[Mg=Fe] sequence only. We find that the most metal-poor stars ([Fe=H]less than or similar to -1) of the HESTIA galaxies exhibit net rotation up to 80 km s (-1), which is consistent with the Aurora population recently identified in the MW. At higher metallicities ([Fe=H] approximate to -0.5 +/- 0.1) we detect a sharp transition (spin-up) from the turbulent phase to a regular disk-like rotation. Di fferent merger debris appear similar in the [Fe=H]-[Mg=Fe] plane, thus making it di fficult to identify individual events. However, combining a set of abundances, and especially stellar age, makes it possible to distinguish between di fferent debris.
The stellar halo in Local Group Hestia simulations
(ASTRONOMY & ASTROPHYSICS, 2023-09-11) Khoperskov, S; Minchev, I; Libeskind, N; Haywood, M; Di Matteo, P; Belokurov, V; Steinmetz, M; Gomez, FA; [et al.]
Recent progress in understanding the assembly history of the Milky Way (MW) is driven by the tremendous amount of high-quality data delivered by Gaia (ESA), revealing a number of substructures potentially linked to several ancient accretion events. In this work we aim to explore the phase-space structure of accreted stars by analysing six M31 /MW analogues from the HESTIA suite of cosmological hydrodynamics zoom-in simulations of the Local Group. We find that all HESTIA galaxies experience a few dozen mergers but only between one and four of those have stellar mass ratios > 0 :2, relative to the host at the time of the merger. Depending on the halo definition, the most massive merger contributes from 20% to 70% of the total stellar halo mass. Individual merger remnants show diverse density distributions at z = 0, significantly overlapping with each other and with the in situ stars in the L-z - E, (V-R , V-phi) and (R; v(phi)) coordinates. Moreover, merger debris often shifts position in the Lz E space with cosmic time due to the galactic mass growth and the non-axisymmetry of the potential. In agreement with previous works, we show that even individual merger debris exhibit a number of distinct L-z-E features. In the (V-R,V-phi) plane, all HESTIA galaxies reveal radially hot, non-rotating or weakly counter-rotating, Gaia-Sausage-like features, which are the remnants of the most recent significant mergers. We find an age gradient in L-z - E space for individual debris, where the youngest stars, formed in the inner regions of accreting systems, deposit to the innermost regions of the host galaxies. The bulk of these stars formed during the last stages of accretion, making it possible to use the stellar ages of the remnants to date the merger event. In action space ( J(r),J(z),J(phi)), merger debris do not appear as isolated substructures, but are instead scattered over a large parameter area and overlap with the in situ stars. We suggest that accreted stars can be best identified using root J(r) > 0.2-0.3 (10(4) kpc km s (-1))(0.5). We also introduce a new, purely kinematic space ( J(z) /J(r)-orbital eccentricity), where di fferent merger debris can be disentangled better from each other and from the in situ stars. Accreted stars have a broad distribution of eccentricities, peaking at epsilon approximate to 0.6 0.9, and their mean eccentricity tends to be smaller for systems accreted more recently.
The stellar halo in Local Group Hestia simulations I. The in situ component and the effect of mergers
(ASTRONOMY & ASTROPHYSICS, 2023-09-11) Khoperskov, S; Minchev, I; Libeskind, N; Haywood, M; Di Matteo, P; Belokurov, V; Steinmetz, M; Gomez, FA; [et al.]
Theory suggests that mergers play an important role in shaping galactic discs and stellar haloes, which was observationally confirmed in the Milky Way (MW) thanks to Gaia data. In this work, aiming to probe the contribution of mergers to the in situ stellar halo formation, we analyse six M31 and MW analogues from the HESTIA suite of cosmological hydrodynamical zoom-in simulations of the Local Group. We found that all the HESTIA galaxies experience between one to four mergers with stellar mass ratios between 0.2 and 1 relative to the host at the time of the merger. These significant mergers, with a single exception, happened 7 11 Gyr ago. The overall impact of the most massive mergers in HESTIA is clearly seen as a sharp increase in the orbital eccentricity (and a corresponding decrease in the rotational velocity V-phi) of pre-existing disc stars of the main progenitor, thus nicely reproducing the Splash-, Plume-like feature that was discovered in the MW. We do find a correlation between mergers and close pericentric passages of massive satellites and bursts of the star formation in the in situ component. Massive mergers sharply increase the disc velocity dispersion of the in situ stars; however, the latest significant merger often heats up the disc up to the numbers when the contribution of the previous ones is less prominent in the age-velocity dispersion relation. In HESTIA galaxies, the in situ halo is an important component of the inner stellar halo where its fraction is about 30 40%, while in the outer parts it typically does not exceed approximate to 5% beyond 15 kpc from the galactic centre. The simulations suggest that this component of the stellar haloes continues to grow well after mergers conclude; however, the most significant contribution comes from stars that formed recently before the merger. The orbital analysis of the HESTIA galaxies suggests that wedges in R-max Z(max) (apocentre - maximum height from the mid-plane) space are mainly populated by the stars born in between significant mergers.
The VANDELS ESO public spectroscopic survey: The spectroscopic measurements catalogue
(ASTRONOMY & ASTROPHYSICS, 2023-09-29) Talia, M; Schreiber, C; Garilli, B; Pentericci, L; [et al.]
VANDELS is a deep spectroscopic survey, performed with the VIMOS instrument at VLT, aimed at studying in detail the physical properties of high-redshift galaxies. VANDELS targeted similar to 2100 sources at 1 < z < 6.5 in the CANDELS Chandra Deep-Field South (CDFS) and Ultra-Deep Survey (UDS) fields. In this paper, we present the public release of the spectroscopic measurement catalogues from this survey, featuring emission and absorption line centroids, fluxes, and rest-frame equivalent widths obtained through a Gaussian fit, as well as a number of atomic and molecular indices (e.g. Lick) and continuum breaks (e.g. D4000), and including a correction to be applied to the error spectra. We describe the measurement methods and the validation of the codes that were used.
The VANDELS survey: the ionizing properties of star-forming galaxies at 3=z=5 using deep rest-frame ultraviolet spectroscopy
(MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 2023-05-11) Saldana-Lopez, A; Schaerer, D; Chisholm, J; Calabrò, A; [et al.]
The physical properties of Epoch of Reionization (EoR) galaxies are still poorly constrained by observations. To better understand the ionizing properties of galaxies in the EoR, we investigate deep, rest-frame ultraviolet (UV) spectra of similar or equal to 500 star-forming galaxies at 3 = z & = 5 selected from the public ESO-VANDELS spectroscopic survey. The absolute ionizing photon escape fraction ($f_{\rm esc}<^>{\rm abs}$, i.e. the ratio of leaking against produced ionizing photons) is derived by combining absorption line measurements with estimates of the UV attenuation. The ionizing production efficiency (?(ion), i.e. the number of ionizing photons produced per non-ionizing UV luminosity) is calculated by fitting the far-UV (FUV) stellar continuum of the VANDELS galaxies. We find that the $f_{\rm esc}<^>{\rm abs}$ and ?(ion) parameters increase towards low-mass, blue UV-continuum slopes and strong Ly a emitting galaxies, and both are slightly higher-than-average for the UV-faintest galaxies in the sample. Potential Lyman Continuum Emitters (LCEs, $f_{\rm esc}<^>{\rm abs} \ge 5{{\ \rm \, per\ cent}}$) and selected Lyman Alpha Emitters (LAEs, W-Lya <= -20 angstrom) show systematically higher ?(ion) (log ?(ion)(Hz erg(-1)) approximate to 25.38, 25.41) than non-LCEs and non-LAEs (log ?(ion)(Hz erg(-1)) approximate to 25.18, 25.14) at similar UV magnitudes. This indicates very young underlying stellar populations (approximate to 10 Myr) at relatively low metallicities (approximate to 0.2 Z(circle dot)). The FUV non-ionizing spectra of potential LCEs is characterized by blue UV slopes (<=-2), enhanced Ly a emission (<=-25 angstrom), strong UV nebular lines (e.g. high ${\rm C\, \small {IV}}$1550/${\rm C\, \small {III}}$1908 >= 0.75 ratios), and weak absorption lines (<= 1 angstrom). The latter suggests the existence of low gas-column-density channels in the interstellar medium, which enables the escape of ionizing photons. By comparing our VANDELS results against other surveys in the literature, our findings imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass, and dustless galaxies.
Using [Ne v]/[Ne iii] to Understand the Nature of Extreme-ionization Galaxies
(ASTROPHYSICAL JOURNAL, 2023-08-01) Cleri, NJ; Olivier, GM; Hutchison, TA; Papovich, C; [et al.]
Spectroscopic studies of extreme-ionization galaxies (EIGs) are critical to our understanding of exotic systems throughout cosmic time. These EIGs exhibit spectral features requiring >54.42 eV photons: the energy needed to ionize helium into He2+ fully and emit He ii recombination lines. Spectroscopic studies of EIGs can probe exotic stellar populations or accretion onto intermediate-mass black holes (& SIM;10(2)-10(5) M (& ODOT;)), which are the possibly key contributors to the reionization of the Universe. To facilitate the use of EIGs as probes of high-ionization systems, we focus on ratios constructed from several rest-frame UV/optical emission lines: [O iii] & lambda;5008, H & beta;, [Ne iii] & lambda;3870, [O ii] & lambda; & lambda;3727, 3729, and [Ne v] & lambda;3427. These lines probe the relative intensity at energies of 35.12, 13.62, 40.96, 13.62, and 97.12 eV, respectively, covering a wider range of ionization than traced by other common rest-frame UV/optical techniques. We use the ratios of these lines ([Ne v]/[Ne iii] & EQUIV; Ne53, [O iii]/H & beta;, and [Ne iii]/[O ii]), which are nearby in wavelength, mitigating the effects of dust attenuation and uncertainties in flux calibration. We make predictions from photoionization models constructed from Cloudy that use a broad range of stellar populations and black hole accretion models to explore the sensitivity of these line ratios to changes in the ionizing spectrum. We compare our models to observations from the Hubble Space Telescope and JWST of galaxies with strong high-ionization emission lines at z & SIM; 0, z & SIM; 2, and 5 < z < 8.5. We show that the Ne53 ratio can separate galaxies with ionization from normal stellar populations from those with active galactic nuclei and even exotic Population III models. We introduce new selection methods to identify galaxies with photoionization driven by Population III stars or intermediate-mass black hole accretion disks that could be identified in upcoming high-redshift spectroscopic surveys.