اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe Giant Gemini GMOS survey of z>4.4 quasars - I. Measuring the mean free path across cosmic time
45
0
0.0
(
0
)
تأليف
Gabor Worseck
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We have obtained spectra of 163 quasars at $z_mathrm{em}>4.4$ with the Gemini Multi Object Spectrometers on the Gemini North and South telescopes, the largest publicly available sample of high-quality, low-resolution spectra at these redshifts. From this homogeneous data set, we generated stacked quasar spectra in three redshift intervals at $zsim 5$. We have modelled the flux below the rest-frame Lyman limit ($lambda_mathrm{r}<912$AA) to assess the mean free path $lambda_mathrm{mfp}^{912}$ of the intergalactic medium to HI-ionizing radiation. At mean redshifts $z_mathrm{q}=4.56$, 4.86 and 5.16, we measure $lambda_mathrm{mfp}^{912}=(22.2pm 2.3, 15.1pm 1.8, 10.3pm 1.6)h_{70}^{-1}$ proper Mpc with uncertainties dominated by sample variance. Combining our results with $lambda_mathrm{mfp}^{912}$ measurements from lower redshifts, the data are well modelled by a simple power-law $lambda_mathrm{mfp}^{912}=A[(1+z)/5]^eta$ with $A=(37pm 2)h_{70}^{-1}$ Mpc and $eta = -5.4pm 0.4$ between $z=2.3$ and $z=5.5$. This rapid evolution requires a physical mechanism -- beyond cosmological expansion -- which reduces the cosmic effective Lyman limit opacity. We speculate that the majority of HI Lyman limit opacity manifests in gas outside galactic dark matter haloes, tracing large-scale structures (e.g. filaments) whose average density (and consequently neutral fraction) decreases with cosmic time. Our measurements of the strongly redshift-dependent mean free path shortly after the completion of HI reionization serve as a valuable boundary condition for numerical models thereof. Having measured $lambda_mathrm{mfp}^{912}approx 10$ Mpc at $z=5.2$, we confirm that the intergalactic medium is highly ionized by that epoch and that the redshift evolution of the mean free path does not show a break that would indicate a recent end to HI reionization.
قيم البحث
اقرأ أيضاً
We present the results of SPT-GMOS, a spectroscopic survey with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South. The targets of SPT-GMOS are galaxy clusters identified in the SPT-SZ survey, a millimeter-wave survey of 2500 squ. deg. of th
e southern sky using the South Pole Telescope (SPT). Multi-object spectroscopic observations of 62 SPT-selected galaxy clusters were performed between January 2011 and December 2015, yielding spectra with radial velocity measurements for 2595 sources. We identify 2243 of these sources as galaxies, and 352 as stars. Of the galaxies, we identify 1579 as members of SPT-SZ galaxy clusters. The primary goal of these observations was to obtain spectra of cluster member galaxies to estimate cluster redshifts and velocity dispersions. We describe the full spectroscopic dataset and resulting data products, including galaxy redshifts, cluster redshifts and velocity dispersions, and measurements of several well-known spectral indices for each galaxy: the equivalent width, W, of [O II] 3727,3729 and H-delta, and the 4000A break strength, D4000. We use the spectral indices to classify galaxies by spectral type (i.e., passive, post-starburst, star-forming), and we match the spectra against photometric catalogs to characterize spectroscopically-observed cluster members as a function of brightness (relative to m*). Finally, we report several new measurements of redshifts for ten bright, strongly-lensed background galaxies in the cores of eight galaxy clusters. Combining the SPT-GMOS dataset with previous spectroscopic follow-up of SPT-SZ galaxy clusters results in spectroscopic measurements for >100 clusters, or ~20% of the full SPT-SZ sample.
Giant molecular clouds (GMCs) are well-studied in the local Universe, however, exactly how their properties vary during galaxy evolution is poorly understood due to challenging resolution requirements, both observational and computational. We present
the first time-dependent analysis of giant molecular clouds in a Milky Way-like galaxy and an LMC-like dwarf galaxy of the FIRE-2 (Feedback In Realistic Environments) simulation suite, which have sufficient resolution to predict the bulk properties of GMCs in cosmological galaxy formation self-consistently. We show explicitly that the majority of star formation outside the galactic center occurs within self-gravitating gas structures that have properties consistent with observed bound GMCs. We find that the typical cloud bulk properties such as mass and surface density do not vary more than a factor of 2 in any systematic way after the first Gyr of cosmic evolution within a given galaxy from its progenitor. While the median properties are constant, the tails of the distributions can briefly undergo drastic changes, which can produce very massive and dense self-gravitating gas clouds. Once the galaxy forms, we identify only two systematic trends in bulk properties over cosmic time: a steady increase in metallicity produced by previous stellar populations and a weak decrease in bulk cloud temperatures. With the exception of metallicity we find no significant differences in cloud properties between the Milky Way-like and dwarf galaxies. These results have important implications for cosmological star and star cluster formation and put especially strong constraints on theories relating the stellar initial mass function to cloud properties.
This work investigates the alignment of galactic spins with the cosmic web across cosmic time using the cosmological hydrodynamical simulation Horizon-AGN. The cosmic web structure is extracted via the persistent skeleton as implemented in the DISPER
SE algorithm. It is found that the spin of low-mass galaxies is more likely to be aligned with the filaments of the cosmic web and to lie within the plane of the walls while more massive galaxies tend to have a spin perpendicular to the axis of the filaments and to the walls. The mass transition is detected with a significance of 9 sigmas. This galactic alignment is consistent with the alignment of the spin of dark haloes found in pure dark matter simulations and with predictions from (anisotropic) tidal torque theory. However, unlike haloes, the alignment of low-mass galaxies is weak and disappears at low redshifts while the orthogonal spin orientation of massive galaxies is strong and increases with time, probably as a result of mergers. At fixed mass, alignments are correlated with galaxy morphology: the high-redshift alignment is dominated by spiral galaxies while elliptical centrals are mainly responsible for the perpendicular signal. These predictions for spin alignments with respect to cosmic filaments and unprecendently walls are successfully compared with existing observations. The alignment of the shape of galaxies with the different components of the cosmic web is also investigated. A coherent and stronger signal is found in terms of shape at high mass. The two regimes probed in this work induce competing galactic alignment signals for weak lensing, with opposite redshift and luminosity evolution. Understanding the details of these intrinsic alignments will be key to exploit future major cosmic shear surveys like Euclid or LSST.
It is difficult to reconcile the observed evolution of the star formation rate versus stellar mass (SFR-M*) relation with expectations from current hierarchical galaxy formation models. The observed SFR-M* relation shows a rapid rise in SFR(M*) from
z=0-2, and then a surprisingly lack of amplitude evolution out to z~6+. Hierarchical models of galaxy formation match this trend qualitatively but not quantitatively, with a maximum discrepancy of ~x3 in SFR at z~2. One explanation, albeit radical, is that the IMF becomes modestly weighted towards massive stars out to z~2, and then evolves back towards its present-day form by z~4 or so. We observe that this redshift trend mimics that of the cosmic fraction of obscured star formation, perhaps hinting at a physical connection. Such IMF evolution would concurrently go towards explaining persistent discrepancies between integrated measures of star formation and present-day stellar mass or cosmic colors.
The quasar sample of the fourteenth data release of the Sloan Digital Sky Survey (SDSS-IV DR14) is used to determine the cosmic homogeneity scale in the redshift range $0.80<z<2.24$. We divide the sample into 4 redshift bins, each one with $N_{rm q}
geq 19,000$ quasars, spanning the whole redshift coverage of the survey and use two correlation function estimators to measure the scaled counts-in-spheres and its logarithmic derivative, i.e., the fractal correlation dimension, $D_2$. Using the $Lambda$CDM cosmology as the fiducial model, we first estimate the redshift evolution of quasar bias and then the homogeneity scale of the underlying matter distribution $r_{rm{hom}}^{rm{m}}$. We find that $r_{rm{hom}}^{rm{m}}$ exhibits a decreasing trend with redshift and that the values obtained are in good agreement with the $Lambda$CDM prediction over the entire redshift interval studied. We, therefore, conclude that the large-scale homogeneity assumption is consistent with the largest spatial distribution of quasars currently available
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
