- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
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
-
MASSIV: Mass Assembly Survey with SINFONI in VVDS
摘要： Aims. The MASSIV (Mass Assembly Survey with SINFONI in VVDS) project aims at finding constraints on the different processes involved in galaxy evolution. This study proposes to improve understanding of the galaxy mass assembly through chemical evolution using metallicity as a tracer of the star formation and interaction history. Methods. We analysed the full sample of MASSIV galaxies for which a metallicity estimate has been possible, the 48 star-forming galaxies at z ～ 0.9?1.8, and computed the integrated values of some of the fundamental parameters, such as stellar mass, metallicity, and star formation rate (SFR). The sample of star-forming galaxies at similar redshifts from zCOSMOS was also combined with the MASSIV sample. We studied the cosmic evolution of the mass-metallicty relation, together with the effect of close environment and galaxy kinematics on this relation. We then focussed on the so-called fundamental metallicity relation and other relations between stellar mass, SFR, and metallicity. We investigated whether these relations are really fundamental, i.e. if they do not evolve with redshift. Results. The MASSIV galaxies follow the expected mass-metallicity relation for their median redshift. We find, however, a significant difference between isolated and interacting galaxies as found for local galaxies: interacting galaxies tend to have a lower metallicity. The study of the relation between stellar mass, SFR, and metallicity gives such large scattering for our sample, even combined with zCOSMOS, that it is difficult to confirm any fundamental relation.
关键词： galaxies: abundances,galaxies: high-redshift,galaxies: fundamental parameters,galaxies: evolution
更新于2025-09-23 15:22:29
-
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
-
Near-infrared spectroscopic indices for unresolved stellar populations
摘要： Context. A new generation of spectral synthesis models has been developed in recent years, but there is no matching set of template galaxy spectra, in terms of quality and resolution, for testing and refining the new models. Aims. Our main goal is to find and calibrate new near-infrared spectral indices along the Hubble sequence of galaxies which will be used to obtain additional constraints to the population analysis based on medium-resolution integrated spectra of galaxies. Methods. Spectra of previously studied and well-understood galaxies with relatively simple stellar populations (e.g., ellipticals or bulge dominated galaxies) are needed to provide a baseline data set for spectral synthesis models. Results. X-shooter spectra spanning the optical and infrared wavelengths (350–2400 nm) of bright nearby elliptical galaxies with a resolving power of R ～ 4000–5400 were obtained. Heliocentric systemic velocity, velocity dispersion, and Mg, Fe, and Hβ line-strength indices are presented. Conclusions. We present a library of very-high-quality spectra of galaxies covering a large range of age, metallicity, and morphological type. Such a dataset of spectra will be crucial to addressing important questions of the modern investigation concerning galaxy formation and evolution.
关键词： galaxies: formation,galaxies: stellar content,infrared: galaxies,surveys,galaxies: abundances
更新于2025-09-23 15:19:57
-
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