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Photoionization models for extreme Ly <i>α λ</i> 1216 and Hell <i>λ</i> 1640 line ratios in quasar halos, and PopIII vs. AGN diagnostics
摘要： Aims. We explore potential mechanisms to produce extremely high Lyα/HeII ?ux ratios, or to enhance the observed number of Lyα photons per incident ionizing photon, in extended active galactic nucleus (AGN) photoionized nebulae at high-redshift. Methods. We computed models to simulate, in the low density regime, photoionization of interstellar gas by the radiation ?eld of a luminous AGN. We have explored the impact of ionization parameter, gas metallicity, ionizing spectrum, electron energy distribution, and cloud viewing angle on the relative ?uxes of Lyα, HeII and other lines, and on the observed number of Lyα photons per incident ionizing photon. We have compared our model results with recent observations of quasar Lyα halos at z ～ 3.5. Results. Low ionization parameter, a relatively soft or ?ltered ionizing spectrum, low gas metallicity, κ-distributed electron energies, or re?ection of Lyα photons by neutral hydrogen can all result in signi?cantly enhanced Lyα relative to other lines (≥10%), with log Lyα/HeII reaching values of up to 4.6. In the cases of low gas metallicity, re?ection by HI, or a hard or ?ltered ionizing spectrum, the observed number of Lyα photons per incident ionizing photon is itself signi?cantly enhanced above the nominal Case B value of 0.66 due to collisional excitation, reaching values as high as 5.3 in an “extreme case” model which combines several of these e?ects. We ?nd that at low gas metallicity (e.g. Z/Z(cid:12) = 0.1) the production of Lyα photons is predominantly via collisional excitation rather than by recombination. In addition, we ?nd that the collisional excitation of Lyα becomes much more e?cient if the ionizing continuum spectrum has been pre-?ltered through an optically thin screen of gas closer to the AGN (e.g. by a wide-angle, feedback-driven out?ow). We also show that the Lyα and HeII emission line ratios of a sample of previously studied quasars at z ～ 3.5 are consistent with AGN-photoionization of gas with moderate to low metallicity and/or low ionization parameter, without requiring exotic ionization or excitation mechanisms such as strong line-transfer e?ects. In addition, we present a set of UV-optical diagnostic diagrams to distinguish between photoionization by Pop III stars and photoionization by an AGN.
关键词： quasars: emission lines,galaxies: active,galaxies: ISM,galaxies: abundances,galaxies: high-redshift
更新于2025-09-23 15:23:52
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ALMA-backed NIR high resolution integral field spectroscopy of the NUGA galaxy NGC 1433
摘要： Aims. We present the results of near-infrared (NIR) H- and K-band European Southern Observatory SINFONI integral field spectroscopy (IFS) of the Seyfert 2 galaxy NGC 1433. We investigate the central 500 pc of this nearby galaxy, concentrating on excitation conditions, morphology, and stellar content. NGC 1433 was selected from our extended NUGA(-south) sample, which was additionally observed with the Atacama Large Millimeter/submillimeter Array (ALMA). NGC 1433 is a ringed, spiral galaxy with a main stellar bar in roughly east–west direction (PA 94?) and a secondary bar in the nuclear region (PA 31?). Several dusty filaments are detected in the nuclear region with the Hubble Space Telescope. ALMA detects molecular CO emission coinciding with these filaments. The active galactic nucleus is not strong and the galaxy is also classified as a low-ionization emission-line region (LINER). Methods. The NIR is less affected by dust extinction than optical light and is sensitive to the mass-dominating stellar populations. SINFONI integral field spectroscopy combines NIR imaging and spectroscopy, allowing us to analyse several emission and absorption lines to investigate the stellar populations and ionization mechanisms over the 10'' × 10'' field of view (FOV). Results. We present emission and absorption line measurements in the central kpc of NGC 1433. We detect a narrow Balmer line and several H2 lines. We find that the stellar continuum peaks in the optical and NIR in the same position, indicating that there is no covering of the center by a nuclear dust lane. A strong velocity gradient is detected in all emission lines at that position. The position angle of this gradient is at 155? whereas the galactic rotation is at a position angle of 201?. Our measures of the molecular hydrogen lines, hydrogen recombination lines, and [Fe II] indicate that the excitation at the nucleus is caused by thermal excitation, i.e., shocks that can be associated with active galactic nuclei emission, supernovae, or outflows. The line ratios [Fe II]/Paβ and H2/Brγ show a Seyfert to LINER identification of the nucleus. We do not detect high star formation rates in our FOV. The stellar continuum is dominated by spectral signatures of red-giant M stars. The stellar line-of-sight velocity follows the galactic field whereas the light continuum follows the nuclear bar. Conclusions. The dynamical center of NGC 1433 coincides with the optical and NIR center of the galaxy and the black hole position. Within the central arcsecond, the molecular hydrogen and the 12CO(3?2) emissions – observed in the NIR and in the submillimeter with SINFONI and ALMA, respectively – are indicative for a nuclear outflow originating from the galaxy’s SMBH. A small circumnuclear disk cannot be fully excluded. Derived gravitational torques show that the nuclear bar is able to drive gas inward to scales where viscosity torques and dynamical friction become important. The black hole mass, derived using stellar velocity dispersion, is ～107 M☉.
关键词： galaxies: nuclei,galaxies: individual: NGC 1433,galaxies: active,infrared: galaxies,galaxies: ISM,galaxies: kinematics and dynamics
更新于2025-09-23 15:22:29
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Neutral gas properties of Lyman continuum emitting galaxies: Column densities and covering fractions from UV absorption lines
摘要： Context. The processes allowing the escape of ionizing photons from galaxies into the intergalactic medium are poorly known. Aims. To understand how Lyman continuum (LyC) photons escape galaxies, we constrain the H I covering fractions and column densities using ultraviolet (UV) H I and metal absorption lines of 18 star-forming galaxies that have Lyman series observations. Nine of these galaxies are confirmed LyC emitters. Methods. We fit the stellar continuum, dust attenuation, metal, and H I properties to consistently determine the UV attenuation, as well as the column densities and covering factors of neutral hydrogen and metals. We used synthetic interstellar absorption lines to explore the systematics of our measurements. Then we applied our method to the observed UV spectra of low-redshift and z ~ 3 galaxies. Results. The observed H I lines are found to be saturated in all galaxies. An indirect approach using O I column densities and the observed O/H abundances yields H I column densities of log(NH I) ~ 18.6 - 20 cm^{-2}. These columns are too high to allow the escape of ionizing photons. We find that the known LyC leakers have H I covering fractions less than unity. Ionizing photons escape through optically thin channels in a clumpy interstellar medium. Our simulations confirm that the H I covering fractions are accurately recovered. The Si II and H I covering fractions scale linearly, in agreement with observations from stacked Lyman break galaxy spectra at z ~ 3. Thus, with an empirical correction, the Si II absorption lines can also be used to determine the H I coverage. Finally, we show that a consistent fitting of dust attenuation, continuum, and absorption lines is required to properly infer the covering fraction of neutral gas and subsequently to infer the escape fraction of ionizing radiation. Conclusions. These measurements can estimate the LyC escape fraction, as we demonstrate in a companion paper.
关键词： ISM: abundances,dark ages, reionization, first stars,ultraviolet: ISM,ISM: lines and bands,dust, extinction,galaxies: ISM
更新于2025-09-23 15:22:29
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The GALEX Ultraviolet Virgo Cluster Survey (GUViCS)
摘要： We study the role of the environment on galaxy evolution using a sample of 868 galaxies in the Virgo cluster and in its surrounding regions that are selected from the GALEX Ultraviolet Virgo Cluster Survey (GUViCS) with the purpose of understanding the origin of the red sequence in dense environments. The sample spans a wide range in morphological types (from dwarf ellipticals to Im and BCD) and stellar masses (107 (cid:2) Mstar (cid:2) 1011.5 M(cid:3)). We collected multifrequency data covering the whole electromagnetic spectrum for most of the galaxies, including UV, optical, mid- and far-infrared imaging data, as well as optical and HI spectroscopic data. We ?rst identify the di?erent dynamical substructures that compose the Virgo cluster, and we calculate the local density of galaxies using di?erent methods. We then study the distribution of galaxies belonging to the red sequence, the green valley, and the blue cloud within the di?erent cluster substructures or as a function of galaxy density. Our analysis indicates that all the most massive galaxies (Mstar (cid:3) 1011 M(cid:3)) are slow rotators and are the dominant galaxies of the di?erent cluster substructures, which are generally associated with a di?use X-ray emission. They are probably the result of major merging events that occurred at early epochs, as also indicated by their very old stellar populations. Slow rotators of lower stellar mass (108.5 (cid:2) Mstar (cid:2) 1011 M(cid:3)) are also preferentially located within the di?erent high-density substructures of the cluster. Their position in the velocity space indicates that they are virialised within the cluster; thus, they are Virgo members since its formation. They have been shaped by gravitational perturbations occurring within the infalling groups that later form the cluster (pre-processing). On the contrary, low-mass star-forming systems are extremely rare in the inner regions of the Virgo cluster A, where the density of the intergalactic medium is at its maximum. Our ram pressure stripping models consistently indicate that these star-forming systems can be rapidly deprived of their interstellar medium during their interaction with the intergalactic medium. The lack of gas quenches their star-formation activity transforming them into quiescent dwarf ellipticals. This mild transformation does not perturb the kinematic properties of these galaxies, which still have rotation curves typical of star-forming systems.
关键词： galaxies: interactions,galaxies: star formation,galaxies: clusters: general,galaxies: clusters: individual: Virgo,galaxies: ISM,galaxies: evolution
更新于2025-09-23 15:21:21
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The MUSE <i>Hubble</i> Ultra Deep Field Survey
摘要： The physical origin of the near-ultraviolet Mg ii emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. We explore the nebular and physical properties of a sample of 381 galaxies between 0.70 < z < 2.34 drawn from the MUSE Hubble Ultra Deep Survey. The spectra of these galaxies show a wide variety of profiles of the Mg ii λλ2796, 2803 resonant doublet, from absorption to emission. We present a study on the main drivers for the detection of Mg ii emission in galaxy spectra. By exploiting photoionization models, we verified that the emission-line ratios observed in galaxies with Mg ii in emission are consistent with nebular emission from Hii regions. From a simultaneous analysis of MUSE spectra and ancillary Hubble Space Telescope information through spectral energy distribution fitting, we find that galaxies with Mg ii in emission have lower stellar masses, smaller sizes, bluer spectral slopes, and lower optical depth than those with absorption. This leads us to suggest that Mg ii emission is a potential tracer of physical conditions that are not merely related to those of the ionized gas. We show that these differences in Mg ii emission and absorption can be explained in terms of a higher dust and neutral gas content in the interstellar medium (ISM) of galaxies showing Mg ii in absorption, which confirms the extreme sensitivity of Mg ii to the presence of the neutral ISM. We conclude with an analogy between the Mg ii doublet and the Lyα line that lies in their resonant nature. Further investigations with current and future facilities, including the James Webb Space Telescope, are promising because the detection of Mg ii emission and its potential connection with Lyα could provide new insights into the ISM content in the early Universe.
关键词： ultraviolet: ISM,ISM: lines and bands,ultraviolet: galaxies,galaxies: evolution,galaxies: ISM
更新于2025-09-23 15:21:21
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The [CII] 158 <i>μ</i> m line emission in high-redshift galaxies
摘要： Gas is a crucial component of galaxies, providing the fuel to form stars, and it is impossible to understand the evolution of galaxies without knowing their gas properties. The [CII] fine structure transition at 158 μm is the dominant cooling line of cool interstellar gas, and is the brightest of emission lines from star forming galaxies from FIR through metre wavelengths, almost unaffected by attenuation. With the advent of ALMA and NOEMA, capable of detecting [CII]-line emission in high-redshift galaxies, there has been a growing interest in using the [CII] line as a probe of the physical conditions of the gas in galaxies, and as a star formation rate (SFR) indicator at z ≥ 4. In this paper, we have used a semi-analytical model of galaxy evolution (G.A.S.) combined with the photoionisation code CLOUDY to predict the [CII] luminosity of a large number of galaxies (25 000 at z (cid:39) 5) at 4 ≤ z ≤ 8. We assumed that the [CII]-line emission originates from photo-dominated regions. At such high redshift, the CMB represents a strong background and we discuss its effects on the luminosity of the [CII] line. We studied the L[CII]–SFR and L[CII]–Zg relations and show that they do not strongly evolve with redshift from z = 4 and to z = 8. Galaxies with higher [CII] luminosities tend to have higher metallicities and higher SFRs but the correlations are very broad, with a scatter of about 0.5 and 0.8 dex for L[CII]–SFR and L[CII]–Zg, respectively. Our model reproduces the L[CII]–SFR relations observed in high-redshift star-forming galaxies, with [CII] luminosities lower than expected from local L[CII]–SFR relations. Accordingly, the local observed L[CII]–SFR relation does not apply at high-z (z (cid:38) 5), even when CMB effects are ignored. Our model naturally produces the [CII] deficit (i.e. the decrease of L[CII]/LIR with LIR), which appears to be strongly correlated with the intensity of the radiation field in our simulated galaxies. We then predict the [CII] luminosity function, and show that it has a power law form in the range of L[CII] probed by the model (1 × 107–2 × 109 L(cid:12) at z = 6) with a slope α = ?1. The slope is not evolving from z = 4 to z = 8 but the number density of [CII]-emitters decreases by a factor of 20×. We discuss our predictions in the context of current observational estimates on both the differential and cumulative luminosity functions.
关键词： galaxies: high-redshift,galaxies: ISM,galaxies: evolution
更新于2025-09-23 15:21:21
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First survey of Wolf-Rayet star populations over the full extension of nearby galaxies observed with CALIFA
摘要： The search of extragalactic regions with conspicuous presence of Wolf-Rayet (WR) stars outside the Local Group is challenging task owing to the di?culty in detecting their faint spectral features. In this exploratory work, we develop a methodology to perform an automated search of WR signatures through a pixel-by-pixel analysis of integral ?eld spectroscopy (IFS) data belonging to the Calar Alto Legacy Integral Field Area survey, CALIFA. This procedure has been applied to a sample of nearby galaxies spanning a wide range of physical, morphological, and environmental properties. This technique allowed us to build the ?rst catalogue of regions rich in WR stars with spatially resolved information, and enabled us to study the properties of these complexes in a two-dimensional (2D) context. The detection technique is based on the identi?cation of the blue WR bump (around He ii λ4686 ?, mainly associated with nitrogen-rich WR stars; WN) and the red WR bump (around C iv λ5808 ?, mainly associated with carbon-rich WR stars; WC) using a pixel-by-pixel analysis that maximizes the number of independent regions within a given galaxy. We identi?ed 44 WR-rich regions with blue bumps distributed in 25 out of a total of 558 galaxies. The red WR bump was identi?ed only in 5 of those regions. Most of the WR regions are located within one e?ective radius from the galaxy centre, and around one-third are located within ～1 kpc or less from the centre. We found that the majority of the galaxies hosting WR populations in our sample are involved in some kind of interaction process. Half of the host galaxies share some properties with gamma-ray burst (GRB) hosts where WR stars, such as potential candidates to the progenitors of GRBs, are found. We also compared the WR properties derived from the CALIFA data with stellar population synthesis models, and con?rm that simple star models are generally not able to reproduce the observations. We conclude that other e?ects, such as binary star channel (which could extend the WR phase up to 10 Myr), fast rotation, or other physical processes that cause the loss of observed Lyman continuum photons, very likely a?ect the derived WR properties, and hence should be considered when modelling the evolution of massive stars.
关键词： techniques: imaging spectroscopy,galaxies: ISM,galaxies: starburst,stars: Wolf-Rayet
更新于2025-09-23 15:21:21
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The effects of spatial resolution on integral field spectrograph surveys at different redshifts ? The CALIFA perspective
摘要： Context. Over the past decade, 3D optical spectroscopy has become the preferred tool for understanding the properties of galaxies and is now increasingly used to carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass, ATLAS3D, PINGS, and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS, GLACE, and IMAGES have targeted the most luminous galaxies to study mainly their kinematic properties. The on-going CALIFA survey (z ～ 0.02) is the ?rst of a series of upcoming integral ?eld spectroscopy (IFS) surveys with large samples representative of the entire population of galaxies. Others include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at higher redshift. Given the importance of spatial scales in IFS surveys, the study of the e?ects of spatial resolution on the recovered parameters becomes important. Aims. We explore the capability of the CALIFA survey and a hypothetical higher redshift survey to reproduce the properties of a sample of objects observed with better spatial resolution at lower redshift. Methods. Using a sample of PINGS galaxies, we simulated observations at di?erent redshifts. We then studied the behaviour of di?erent parameters as the spatial resolution degrades with increasing redshift. Results. We show that at the CALIFA resolution, we are able to measure and map common observables in a galaxy study: the number and distribution of H ii regions (Hα ?ux structure), the gas metallicity (using the O3N2 method), the gas ionization properties (through the [N ii]/Hα and [O iii]/Hβ line ratios), and the age of the underlying stellar population (using the D4000 index). This supports the aim of the survey to characterise the observable properties of galaxies in the Local Universe. Our analysis of simulated IFS data cubes at higher redshifts highlights the importance of the projected spatial scale per spaxel as the most important ?gure of merit in the design of an integral ?eld survey.
关键词： stars: formation,galaxies: stellar content,galaxies: ISM,galaxies: abundances,techniques: spectroscopic
更新于2025-09-23 15:21:01
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A Window on the Earliest Star Formation: Extreme Photoionization Conditions of a High-ionization, Low-metallicity Lensed Galaxy at <i>z</i> ～ 2*
摘要： We report new observations of SL2S J021737–051329, a lens system consisting of a bright arc at z = 1.84435, magnified ～17× by a massive galaxy at z = 0.65. SL2S0217 is a low-mass (M < 109 Me), low-metallicity (Z ～ 1/20 Ze) galaxy, with extreme star-forming conditions that produce strong nebular UV emission lines in the absence of any apparent outflows. Here we present several notable features from rest-frame UV Keck/LRIS spectroscopy: (1) Very strong narrow emission lines are measured for C IV λλ1548, 1550, He II λ1640, O III] λλ1661, 1666, Si III] λλ1883, 1892, and C III] λλ1907, 1909. (2) Double-peaked Lyα emission is observed with a dominant blue peak and centered near the systemic velocity. (3) The low- and high-ionization absorption features indicate very little or no outflowing gas along the sight line to the lensed galaxy. The relative emission-line strengths can be reproduced with a very high ionization, low-metallicity starburst with binaries, with the exception of He II, which indicates that an additional ionization source is needed. We rule out large contributions from active galactic nuclei and shocks to the photoionization budget, suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models. Therefore, SL2S0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early universe.
关键词： first stars,galaxies: abundances,reionization,gravitational lensing: strong,galaxies: evolution,dark ages,galaxies: ISM
更新于2025-09-10 09:29:36
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Integrated spectroscopy of the <i>Herschel</i> Reference Survey ( <i>Corrigendum</i> )
摘要： We noticed an error in the bisector fitting procedure adopted in our paper. Because of this error, there are some erroneous values in the slopes and intercepts given in Table 6 and in the best fit shown in Figs. 14 and 16. The corrected values and figures are given below. The updated C(Hβ) vs. βGALEX relations (bisector fit) are: C(Hβ) = 1.25 × βGALEX + 1.87; Spearman coefficient ρ = 0.56, shared by HI-deficient and HI-normal galaxies (solid line). A very similar relation is obtained excluding those galaxies hosting an AGN (C(Hβ) = 1.32 × βGALEX + 1.91; Spearman coefficient ρ = 0.61). These errors do not change the major conclusions of the paper.
关键词： galaxies: spiral,galaxies: ISM,dust, extinction,errata, addenda
更新于2025-09-10 09:29:36