分类： 天文学 >> 天文学 提交时间： 2023-02-19
Lance Taylor
Rachel Bezanson
Arjen van der Wel
Alan Pearl
Eric F. Bell
Francesco D'Eugenio
Marijn Franx
Michael V. Maseda
Adam Muzzin
David Sobral
Caroline Straatman
Katherine E. Whitaker
Po-Feng Wu
摘要： We present the first direct spectroscopic measurement of the stellar velocity dispersion function (VDF) for massive quiescent and star-forming galaxies at $0.6 100$ km s$^{-1}$) and extend to star-forming galaxies. We are largely consistent with the high-sigma tail measured from BOSS, and we find that the VDF remains constant from the median redshift of LEGA-C, $z\sim0.8$, to the present day.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Po-Feng Wu
Dylan Nelson
Arjen van der Wel
Annalisa Pillepich
Stefano Zibetti
Rachel Bezanson
Francesco D'Eugenio
Anna Gallazzi
Camilla Pacifici
Caroline M. S. Straatman
Ivana Barišić
Eric F. Bell
Michael V. Maseda
Adam Muzzin
David Sobral
Katherine E. Whitaker
摘要： We present the first comparison of observed stellar continuum spectra of high-redshift galaxies and mock galaxy spectra generated from hydrodynamical simulations. The mock spectra are produced from the IllustrisTNG TNG100 simulation combined with stellar population models and take into account dust attenuation and realistic observational effects (aperture effects and noise). We compare the simulated $D_n4000$ and EW(H$\delta$) of galaxies with $10.5 \leq \log(M_\ast/M_\odot) \leq 11.5$ at $0.6 \leq z \leq 1.0$ to the observed distributions from the LEGA-C survey. TNG100 globally reproduces the observed distributions of spectral indices, implying that the age distribution of galaxies in TNG100 is generally realistic. Yet there are small but significant differences. For old galaxies, TNG100 shows small $D_n4000$ when compared to LEGA-C, while LEGA-C galaxies have larger EW(H$\delta$) at fixed $D_n4000$. There are several possible explanations: 1) LEGA-C galaxies have overall older ages combined with small contributions (a few percent in mass) from younger ($<1$~Gyr) stars, while TNG100 galaxies may not have such young sub-populations; 2) the spectral mismatch could be due to systematic uncertainties in the stellar population models used to convert stellar ages and metallicities to observables. In conclusion, the latest cosmological galaxy formation simulations broadly reproduce the global age distribution of galaxies at $z\sim1$ and, at the same time, the high quality of the latest observed and simulated datasets help constrain stellar population synthesis models as well as the physical models underlying the simulations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Searching in the MaNGA IFU survey, I identify 9 galaxies that have strong Balmer absorption lines and weak nebular emission lines measured from the spectra integrated over the entire IFUs. The spectral features measured from the bulk of the stellar light make these galaxies local analogs of high-redshift spectroscopically-selected post-starburst galaxies, thus, proxies to understand the mechanisms producing post-starburst galaxies at high-redshifts. I present the distributions of absorption-line indices and emission-line strengths, as well as stellar kinematics of these local post-starburst galaxies. Almost all local post-starburst galaxies have central compact emission-line regions at the central $<1$ kpc, mostly powered by weak star-formation activities. The age-sensitive absorption line indices EW(H$\delta$) and Dn4000 indicate that the stellar populations at the outskirts are older. Toy stellar population synthesis models suggest that the entire galaxies are experiencing a rapid decline of star formation with residual star-formation activities at the centers. These features demand that most post-starburst galaxies are the aftermath of highly dissipative processes that drive gas into centers, invoke centrally-concentrated star formation, then quench the galaxies. Meanwhiles, when measurable, post-starburst galaxies have the directions of maximum stellar velocity gradients align with photometric major axes, which suggest against major mergers being the principal driving mechanism, while gas-rich minor mergers are plausible. While directly obtaining the same quality of spatially-resolved spectra of high-redshift post-starburst galaxies is very difficult, finding proper local counterparts provides an alternative to understand quenching processes in the distant Universe.
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