We investigate the chemical properties of local galaxies within a cosmological framework in the hierarchical picture of galaxy formation. To this aim, we use a hierarchical semi-analytic model which includes the contribution from (i) low and intermediate mass stars, (ii) type Ia Supernovae (SNe) and (iii) massive stars. - Abridged - We compare our predictions with available observations in the Milky Way (MW), in local dwarf galaxies and in local ellipticals. For Milky-Way-like galaxies, we can successfully reproduce the [O-Fe] vs [Fe/H] relation observed in disc stars and the stellar metallicity distribution (SMD). For dwarf galaxies, the stellar metallicity vs mass relation is reproduced by assuming that a substantial fraction of the heavy elements is lost through metal-enhanced outflows and a type Ia SN realization probability lower than the one of MW-like galaxies. - Abridged - In ellipticals, the observations indicate higher [alpha/Fe] values in larger galaxies. - Abridged - Our results computed with a standard Salpeter initial mass function (IMF) indicate a flat [alpha/Fe]-sigma relation. However, we suggest a possible solution to this problem and show how, by assuming a star formation-dependent IMF with a slope x=1.35 in systems with star formation rates < 100 M_sun/yr and slightly flatter (i.e. with x=1) in object with stronger star formation, the observed correlation between [alpha/Fe] and sigma can be accounted for on a large velocity dispersion range. Fundamental roles are played also by interaction-triggered starbursts and AGN.
Galaxies throughout the last 12 Gyr of cosmic time follow a single, universal relation that connects their star-formation rates (SFRs), stellar masses ($M_\star$) and chemical abundances. Deviation from these fundamental scaling relations would imply a drastic change in the processes that regulate galaxy evolution. Observations have hinted at the possibility that this relation may be broken in the very early universe. However, until recently, chemical abundances of galaxies could be only measured reliably as far back as redshift $z=3.3$. With JWST, we can now characterize the SFR, $M_\star$, a…
The demographics of dwarf galaxy populations have long been in tension with predictions from the Cold Dark Matter (CDM) paradigm. If primordial density fluctuations were scale-free as predicted, dwarf galaxies should themselves host dark matter subhaloes, the most massive of which may have undergone star formation resulting in dwarf galaxy groups. Ensembles of dwarf galaxies are observed as satellites of more massive galaxies, and there is observational and theoretical evidence to suggest that these satellites at z=0 were captured by the massive host halo as a group. However, the evolution of …
We study the merger history of primordial black holes (PBHs) in a scenario where they represent the dominant dark matter component of a typical dwarf galaxies' core. We investigate the possibility of a sequence of collisions resulting in a hierarchical merger of black holes and look at the final mass spectrum in such {\it clusters}, which initially present a monochromatic (single-mass) PBH population. Our study shows that the merging process results in the transfer of about $40\%$ of the total mass of the core to the merger products regardless of the initial mass of PBHs, with about $5\%$ of e…
Evolution of The Velocity-Dispersion Function of Luminous Red Galaxies: A Hierarchical Bayesian Measurement
本文给出了斯隆数字巡天III（SDSS-III）重子振荡光谱巡天（BOSS）在相对低的光谱信噪比（SNR ~3-5/69 km s^（-1））下观测到的大约430，000个大质量发光红星系（LRGs）的速度色散函数的分级贝叶斯确定。我们边缘化的光谱红移误差，并使用完整的速度色散似然函数为每个星系的速度色散分布参数作为一个函数的绝对星等和红移的自我一致的确定，以及校正宽带的大小误差对我们的合并的影响。参数化的分布在每一个点的亮度红移平面与对数正态形式，我们检测到显着的演变，在更高的红移的分布的宽度向更高的内在散射。使用一个子集的深重新观测的BOSS星系，我们证明了我们的分布参数估计是无偏的，无论光谱信噪比。我们还通过模拟表明，我们的方法没有引入系统参数的红移偏置。我们强调的优势，层次贝叶斯方法的频谱频率论的“堆叠”，并说明我们测得的分布参数可以通过作为信息先验的速度分散测量从个别嘈杂的光谱。
The star formation history and chemical evolution of star forming galaxies in the nearby universe
我们测定了SDSS DR 7中122751个SFG样品的O/H和N/O。对于所有这些星系，我们也确定了它们的形态和SFH使用代码星光。化学丰度与SFH的比较使我们能够以与它们的恒星星族和形态的形成相一致的方式来描述附近宇宙（z < 0.25）的化学演化。在我们的样品中，45%的SFG显示出相对于其金属丰度的氮丰度过剩。我们还发现这种过剩伴随着氧气的缺乏，这表明这可能是有效的星暴风的结果。然而，我们没有发现富氮和贫氮SFG的恒星形成模式的差异。我们的分析表明，它们都是通过在几个Gyr周期内连续的恒星形成爆发来形成恒星的。因此，产生这些星系之间化学差异的似乎是爆发的强度：具有过量氮的星系是那些目前正在经历更强烈爆发的星系，或者在过去经历过更强烈爆发的星系。我们还发现了化学演化过程与星系形成相关的证据：氮过量的星系比没有过量的星系质量更大，有更多的大规模凸起和更早的形态。作为一种可能的解释，我们提出，与星暴风一致的金属损失发生在星系形成期间，当时它们的势阱仍在建立，因此比今天弱，使星暴风更有效，与星系的最终质量无关。与这种解释非常一致，我们也发现了与缩小一致的证据，根据这些证据，更大质量的SFG在质量较小的SFG之前形成。
