Cosmic Metal Enrichment Research Articles

Radio Observations of Six Young Type Ia Supernovae

Type Ia supernovae (SNe Ia) are important cosmological tools, probes of binary star evolution, and contributors to cosmic metal enrichment; yet, a definitive understanding of the binary star systems that produce them remains elusive. Of particular interest is the identity of the mass-donor companion to the exploding carbon–oxygen white dwarf (CO WD). In this work, we present early-time (first observation within 10 days post-explosion) radio observations of six nearby (within 40 Mpc) SNe Ia taken by the Jansky Very Large Array, which are used to constrain the presence of synchrotron emission from the interaction between ejecta and circumstellar material (CSM). The two motivations for these early-time observations are: (1) to constrain the presence of low-density winds and (2) to provide an additional avenue of investigation for those SNe Ia observed to have early-time optical/UV excesses that may be due to CSM interaction. We detect no radio emission from any of our targets. Toward our first aim, these non-detections further increase the sample of SNe Ia that rule out winds from symbiotic binaries and strongly accreting white dwarfs. and discuss the dependence on underlying model assumptions and how our observations represent a large increase in the sample of SNe Ia with low-density wind constraints. For the second aim, we present a radiation hydrodynamics simulation to explore radio emission from an SN Ia interacting with a compact shell of CSM, and find that relativistic electrons cannot survive to produce radio emission despite the rapid expansion of the shocked shell after shock breakout. The effects of model assumptions are discussed for both the wind and compact shell conclusions.

Baryonic post-processing of N-body simulations, with application to fast radio bursts

ABSTRACT Where the cosmic baryons lie in and around galactic dark matter haloes is only weakly constrained. We develop a method to quickly paint on models for their distribution. Our approach uses the statistical advantages of N-body simulations, while painting on the profile of gas around individual haloes in ways that can be motivated by semi-analytic models or zoom-in hydrodynamic simulations of galaxies. Possible applications of the algorithm include extragalactic dispersion measures to fast radio bursts (FRBs), the Sunyaev–Zeldovich effect, baryonic effects on weak lensing, and cosmic metal enrichment. As an initial application, we use this tool to investigate how the baryonic profile of foreground galactic-mass haloes affects the statistics of the dispersion measure (DM) towards cosmological FRBs. We show that the distribution of DM is sensitive to the distribution of baryons in galactic haloes, with viable gas profile models having significantly different probability distributions for DM to a given redshift. We also investigate the requirements to statistically measure the circumgalactic electron profile for FRB analyses that stack DM with impact parameter to foreground galaxies, quantifying the size of the contaminating ‘two-halo’ term from correlated systems and the number of FRBs for a high significance detection. Publicly available python modules implement our CGMBrush algorithm.

The extent of intergalactic metal enrichment from galactic winds during the Cosmic Dawn

ABSTRACT One of the key processes driving galaxy evolution during the Cosmic Dawn is supernova feedback. This likely helps regulate star formation inside of galaxies, but it can also drive winds that influence the large-scale intergalactic medium. Here, we present a simple semi-analytic model of supernova-driven galactic winds and explore the contributions of different phases of galaxy evolution to cosmic metal enrichment in the high-redshift (z ≳ 6) Universe. We show that models calibrated to the observed galaxy luminosity function at z ∼ 6–8 have filling factors $\sim 1{{\%}}$ at z ∼ 6 and $\sim 0.1{{\%}}$ at z ∼ 12, with different star formation prescriptions providing about an order of magnitude uncertainty. Despite the small fraction of space filled by winds, these scenarios predict an upper limit to the abundance of metal-line absorbers in quasar spectra at $z \gtrsim 5$ which is comfortably above that currently observed. We also consider enrichment through winds driven by Pop III star formation in minihalos. We find that these can dominate the total filling factor at $z \gtrsim 10$ and even compete with winds from normal galaxies at z ∼ 6, at least in terms of the total enriched volume. But these regions have much lower overall metallicities, because each one is generated by a small burst of star formation. Finally, we show that Compton cooling of these supernova-driven winds at $z \gtrsim 6$ has only a small effect on the cosmic microwave background.

The rate of Type-Ia supernovae in galaxy clusters and the delay-time distribution out to redshift 1.75

The observed delay-time distribution (DTD) of Type-Ia supernovae (SNe Ia) is a valuable probe of SN Ia progenitors and physics, and of the role of SNe Ia in cosmic metal enrichment. The SN Ia rate in galaxy clusters as a function of cluster redshift is an almost-direct measure of the DTD, but current estimates have been limited out to a mean redshift z=1.1, corresponding to time delays, after cluster star-formation, of over 3.2 Gyr. We analyze data from a Hubble Space Telescope monitoring project of 12 galaxy clusters at z=1.13-1.75, where we discover 29 SNe, and present their multi-band light curves. Based on the SN photometry and the apparent host galaxies, we assess cluster membership and SN type, finding 11 cases that are likely SNe Ia in cluster galaxies and 4 more cases which are possible but not certain cluster SNe Ia. We conduct simulations to estimate the SN detection efficiency, the experiment's completeness, and the photometric errors, and perform photometry of the cluster galaxies to derive the cluster stellar masses. Separating the cluster sample into high-z and low-z bins, we obtain rest-frame SN Ia rates per unit formed stellar mass of $2.2 ^{+2.6}_{-1.3}\times 10^{-13}{\rm yr}^{-1}{\rm M}_\odot^{-1}$ at a mean redshift z=1.25, and $3.5^{+6.6}_{-2.8} \times 10^{-13}{\rm yr}^{-1}{\rm M}_\odot^{-1}$ at z=1.58. Combining our results with previous cluster SN Ia rates, we fit the DTD, now down to delays of 1.5 Gyr, with a power-law dependence, $t^\alpha$, with $\alpha=-1.30^{+0.23}_{-0.16}$. We confirm previous indications for a Hubble-time-integrated SN Ia production efficiency that is several times higher in galaxy clusters than in the field, perhaps caused by a peculiar stellar initial mass function in clusters, or by a higher incidence of binaries that will evolve into SNe Ia.

Mapping metals at high redshift with far-infrared lines

Cosmic metal enrichment is one of the key physical processes regulating galaxy formation and the evolution of the intergalactic medium (IGM). However, determining the metal content of the most distant galaxies has proven so far almost impossible; also, absorption line experiments at $z\sim6$ become increasingly difficult because of instrumental limitations and the paucity of background quasars. With the advent of ALMA, far-infrared emission lines provide a novel tool to study early metal enrichment. Among these, the [CII] line at 157.74 $\mu$m is the most luminous line emitted by the interstellar medium of galaxies. It can also resonant scatter CMB photons inducing characteristic intensity fluctuations ($\Delta I/I_{CMB}$) near the peak of the CMB spectrum, thus allowing to probe the low-density IGM. We compute both [CII] galaxy emission and metal-induced CMB fluctuations at $z\sim 6$ by using Adaptive Mesh Refinement cosmological hydrodynamical simulations and produce mock observations to be directly compared with ALMA BAND6 data ($\nu_{obs}\sim 272$ GHz). The [CII] line flux is correlated with $M_{UV}$ as $\log(F_{peak}/\mu{\rm Jy})=-27.205-2.253\,M_{UV}-0.038\,M_{UV}^2$. Such relation is in very good agreement with recent ALMA observations (e.g. Maiolino et al. 2015; Capak et al. 2015) of $M_{UV}<-20$ galaxies. We predict that a $M_{UV}=-19$ ($M_{UV}=-18$) galaxy can be detected at $4\sigma$ in $\simeq40$ (2000) hours, respectively. CMB resonant scattering can produce $\simeq\pm 0.1\,\mu$Jy/beam emission/absorptions features that are very challenging to be detected with current facilities. The best strategy to detect these signals consists in the stacking of deep ALMA observations pointing fields with known $M_{UV}\simeq-19$ galaxies. This would allow to simultaneously detect both [CII] emission from galactic reionization sources and CMB fluctuations produced by $z\sim6$ metals.

Simulating cosmic metal enrichment by the first galaxies

We study cosmic metal enrichment via AMR hydrodynamical simulations in a (10 Mpc/h)$^3$ volume following the Pop III-Pop II transition and for different Pop III IMFs. We have analyzed the joint evolution of metal enrichment on galactic and intergalactic scales at z=6 and z=4. Galaxies account for <9% of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density ($\Delta$<1), (b) the true intergalactic medium (IGM, 1<$\Delta$<10) and (c) the circumgalactic medium (CGM, 10<$\Delta<10^{2.5}$), the interface between the IGM and galaxies. By z=6 a galactic mass-metallicity relation is established. At z=4, galaxies with a stellar mass $M_*=10^{8.5}M_\odot$ show log(O/H)+12=8.19, consistent with observations. The total amount of heavy elements rises from $\Omega^{SFH}_Z=1.52\, 10^{-6}$ at z=6 to 8.05 $10^{-6}$ at z=4. Metals in galaxies make up to ~0.89 of such budget at z=6; this fraction increases to ~0.95 at z=4. At z=6 (z=4) the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at z=4 a density-metallicity ($\Delta$-Z) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z~$10^{-3.5}$Zsun; in the CGM Z steeply rises with density up to ~$10^{-2}$Zsun. In all diffuse phases a considerable fraction of metals is in a warm/hot (T>$10^{4.5}$K) state. Due to these physical conditions, CIV absorption line experiments can probe only ~2% of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the Pop III star formation history is almost insensitive to the chosen Pop III IMF. Pop III stars are preferentially formed in truly pristine (Z=0) gas pockets, well outside polluted regions created by previous star formation episodes.

Cosmic metal enrichment

AbstractI review the present understanding of the process by which the universe has been enriched in the course of its history with heavy elements produced by stars and transported into the surrounding intergalactic medium. This process goes under the name of “cosmic metal enrichment” and presents some of the most challenging puzzles in present day physical cosmology. These are reviewed along with some proposed explanations that all together form a coherent working scenario.

Feedback and metal enrichment in cosmological smoothed particle hydrodynamics simulations — I. A model for chemical enrichment

We discuss a model for treating chemical enrichment by Type II and Type Ia supernova (SNII and SNIa) explosions in simulations of cosmological structure formation. Our model includes metal-dependent radiative cooling and star formation in dense collapsed gas clumps. Metals are returned into the diffuse interstellar medium by star particles using a local smoothed particle hydrodynamics (SPH) smoothing kernel. A variety of chemical abundance patterns in enriched gas arise in our treatment owing to the different yields and lifetimes of SNII and SNIa progenitor stars. In the case of SNII chemical production, we adopt metal-dependent yields. Because of the sensitive dependence of cooling rates on metallicity, enrichment of galactic haloes with metals can in principle significantly alter subsequent gas infall and the build-up of the stellar components. Indeed, in simulations of isolated galaxies we find that a consistent treatment of metal-dependent cooling produces 25 per cent more stars outside the central region than simulations with a primordial cooling function. In the highly enriched central regions, the evolution of baryons is however not affected by metal cooling, because here the gas is always dense enough to cool. A similar situation is found in cosmological simulations because we include no strong feedback processes which could spread metals over large distances and mix them into unenriched diffuse gas. We demonstrate this explicitly with test simulations which adopt suprasolar cooling functions leading to large changes both in the stellar mass and in the metal distributions. We also find that the impact of metallicity on the star formation histories of galaxies may depend on their particular evolutionary history. Our results hence emphasize the importance of feedback processes for interpreting the cosmic metal enrichment.