اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe interaction-driven starburst contribution to the cosmic star formation rate density
162
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
An increasing amount of observational evidence supports the notion that there are two modes of star formation: a quiescent mode in disk-like galaxies, and a starburst mode, which is generally interpreted as driven by merging. Using a semi-analytic model of galaxy formation, we derive the relative contribution to the cosmic star formation rate density of quiescently starforming and starburst galaxies, predicted under the assumption that starburst events are triggered by galaxy encounters (merging and fly-by kind) during their merging histories. We show that, within this framework, quiescently starforming galaxies dominate the cosmic star formation rate density at all redshifts. The contribution of the burst-dominated starforming galaxies increases with redshift, rising from <5% at low redshift (z<0.1) to ~20% at z>5. We estimated that the fraction of the final (z=0) galaxy stellar mass which is formed through the burst component of star formation is ~10% for 10^10 M_odot<M_*<10^11.5 M_odot. Starburst galaxies, selected according to their distance from the galaxy main sequence, account for ~10% of the star formation rate density in the redshift interval 1.5<z<2.5, i.e. at the cosmic peak of the star formation activity.
قيم البحث
اقرأ أيضاً
The cosmic star formation rate (CSFR), is an important clue to investigate the history of the assembly and evolution of galaxies. Here, we develop a method to study the CSFR from a purely theoretical point of view. Starting from detailed models of ch
emical evolution, we obtain the histories of star formation of galaxies of different morphological types. These histories are then used to determine the luminosity functions of the same galaxies by means of a spectro-photometric code. We obtain the CSFR under different hypothesis. First, we study the hypothesis of a pure luminosity evolution scenario, in which all galaxies are supposed to form at the same redshift and then evolve only in luminosity. Then we consider scenarios in which the number density or the slope of the LFs are assumed to vary with redshift. After comparison with available data we conclude that a pure luminosity evolution does not provide a good fit to the data, especially at very high redshift, although many uncertainties are still present in the data. On the other hand, a variation in the number density of ellipticals and spirals as a function of redshift can provide a better fit to the observed CSFR. We also explore cases of variable slope of the LFs with redshift and variations of number density and slope at the same time. We cannot find any of those cases which can improve the fit to the data respect to the solely number density variation. Finally, we compute the evolution of the average cosmic metallicity in galaxies with redshift.
The under-abundance of very massive galaxies in the universe is frequently attributed to the effect of galactic winds. Although ionized galactic winds are readily observable most of the expelled mass is likely in cooler atomic and molecular phases. E
xpanding molecular shells observed in starburst systems such as NGC 253 and M 82 may facilitate the entrainment of molecular gas in the wind. While shell properties are well constrained, determining the amount of outflowing gas emerging from such shells and the connection between this gas and the ionized wind requires spatial resolution <100 pc coupled with sensitivity to a wide range of spatial scales, hitherto not available. Here we report observations of NGC 253, a nearby starburst galaxy (D~3.4 Mpc) known to possess a wind, which trace the cool molecular wind at 50 pc resolution. At this resolution the extraplanar molecular gas closely tracks the H{alpha} filaments, and it appears connected to molecular expanding shells located in the starburst region. These observations allow us to directly measure the molecular outflow rate to be > 3 Msun/yr and likely ~9 Msun/yr. This implies a ratio of mass-outflow rate to star formation rate of at least {eta}~1-3, establishing the importance of the starburst-driven wind in limiting the star formation activity and the final stellar content.
Observations of high-z galaxies and gamma-ray bursts now allow for empirical studies during reionization. However, even deep surveys see only the brightest galaxies at any epoch and must extrapolate to arbitrary lower limits to estimate the total rat
e of star formation. We first argue that the galaxy populations seen in LBG surveys yield a GRB rate at z > 8 that is an order of magnitude lower than observed. We find that integrating the inferred UV luminosity functions down to M_UV ~ -10 brings LBG- and GRB-inferred SFR density values into agreement up to z ~ 8. GRBs, however, favor a far larger amount of as yet unseen star formation at z > 9. We suggest that the SFR density may only slowly decline out to z ~ 11, in accord with WMAP and Planck reionization results, and that GRBs may be useful in measuring the scale of this multitude of dwarf galaxies.
We investigate the evolution of the star formation rate (SFR)-density relation in the Extended Chandra Deep Field South (ECDFS) and the Great Observatories Origin Deep Survey (GOODS) fields up to z~1.6. In addition to the traditional method, in which
the environment is defined according to a statistical measurement of the local galaxy density, we use a dynamical approach, where galaxies are classified according to three different environment regimes: group, filament-like, and field. Both methods show no evidence of a SFR-density reversal. Moreover, group galaxies show a mean SFR lower than other environments up to z~1, while at earlier epochs group and field galaxies exhibit consistent levels of star formation (SF) activity. We find that processes related to a massive dark matter halo must be dominant in the suppression of the SF below z~1, with respect to purely density-related processes. We confirm this finding by studying the distribution of galaxies in different environments with respect to the so-called Main Sequence (MS) of star-forming galaxies. Galaxies in both group and filament-like environments preferentially lie below the MS up to z~1, with group galaxies exhibiting lower levels of star-forming activity at a given mass. At z>1, the star-forming galaxies in groups reside on the MS. Groups exhibit the highest fraction of quiescent galaxies up to z~1, after which group, filament-like, and field environments have a similar mix of galaxy types. We conclude that groups are the most efficient locus for star-formation quenching. Thus, a fundamental difference exists between bound and unbound objects, or between dark matter haloes of different masses.
Although Galactic cosmic rays (protons and nuclei) are widely believed to be dominantly accelerated by the winds and supernovae of massive stars, definitive evidence of this origin remains elusive nearly a century after their discovery [1]. The activ
e regions of starburst galaxies have exceptionally high rates of star formation, and their large size, more than 50 times the diameter of similar Galactic regions, uniquely enables reliable calorimetric measurements of their potentially high cosmic-ray density [2]. The cosmic rays produced in the formation, life, and death of their massive stars are expected to eventually produce diffuse gamma-ray emission via their interactions with interstellar gas and radiation. M 82, the prototype small starburst galaxy, is predicted to be the brightest starburst galaxy in gamma rays [3, 4]. Here we report the detection of >700 GeV gamma rays from M 82. From these data we determine a cosmic-ray density of 250 eV cm-3 in the starburst core of M 82, or about 500 times the average Galactic density. This result strongly supports that cosmic-ray acceleration is tied to star formation activity, and that supernovae and massive-star winds are the dominant accelerators.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
