Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRed & Dead CANDELS: massive passive galaxies at the dawn of the Universe
129
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We search the five CANDELS fields (COSMOS, EGS, GOODS-North, GOODS-South and UDS) for passively evolving a.k.a. red and dead massive galaxies in the first 2 Gyr after the Big Bang, integrating and updating the work on GOODS-South presented in our previous paper. We perform SED-fitting on photometric data, with top-hat star-formation histories to model an early and abrupt quenching, and using a probabilistic approach to select only robust candidates. Using libraries without (with) spectral lines emission, starting from a total of more than 20,000 $z>3$ sources we end up with 102 (40) candidates, including one at $z=6.7$. This implies a minimal number density of $1.73 pm 0.17 times 10^{-5}$ ($6.69 pm 1.08 times 10^{-6}$) Mpc$^{-3}$ for $3<z<5$; applying a correction factor to account for incompleteness yields $2.30 pm 0.20 times 10^{-5}$. We compare these values with those from five recent hydrodynamical cosmological simulations, finding a reasonable agreement at $z<4$; tensions arise at earlier epochs. Finally, we use the star-formation histories from the best-fit models to estimate the contribution of the high-redshift passive galaxies to the global Star Formation Rate Density during their phase of activity, finding that they account for $sim5-10%$ of the total star formation at $3<z<8$, despite being only $sim0.5%$ of the total in number. The resulting picture is that early and strong star formation activity, building massive galaxies on short timescales and followed by a quick and abrupt quenching, is a rare but crucial phenomenon in the early Universe: the evolution of the cosmos must be heavily influenced by the short but powerful activity of these pristine monsters.
rate research
Read More
At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation(1-4). It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions(5,6), but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies(7). Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which surprisingly turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst(8). The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo(9). This result confirms previous indirect indications(10-13) that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.
The selection of red, passive galaxies in the early Universe is very challenging, especially beyond z~3, and it is crucial to constrain theoretical modelling of the processes responsible for their rapid assembly and abrupt shut-down of the star formation. We present here the analysis of ALMA archival observations of 26 out of the 30 galaxies in the deep CANDELS GOODS-South field that we identified as passive at z~3-5 by means of a careful and conservative SED fitting analysis. ALMA data are used to verify the potential contamination from red, dusty but star--forming sources that could enter the sample due to similar optical--nearIR colours. With the exception of a few marginal detections at <3sigma, we could only infer upper limits, both on individual sources and on the stacks. We translated the ALMA continuum measurements into corresponding SFRs, using a variety of far-IR models. These SFRs are compared with those predicted by secondary star-forming solutions of the optical fits and with the expected position of the star formation Main Sequence. This analysis confirms the passive nature of 9 candidates with high confidence and suggests that the classification is correct for at least half of the sample in a statistical sense. For the remaining sources the analysis remain inconclusive because available ALMA data is not deep enough, although the stacking results corroborate their passive nature. Despite the uncertainties, this work provides decisive support to the existence of passive galaxies beyond z~3.
We investigate the star formation histories (SFHs) of massive red spiral galaxies with stellar mass $M_ast>10^{10.5}M_odot$, and make comparisons with blue spirals and red ellipticals of similar masses. We make use of the integral field spectroscopy from the SDSS-IV/DR15 MaNGA sample, and estimate spatially resolved SFHs and stellar population properties of each galaxy by applying a Bayesian spectral fitting code to the MaNGA spectra. We find that both red spirals and red ellipticals have experienced only one major star formation episode at early times, and the result is independent of the adopted SFH model. On average, more than half of their stellar masses were formed $>$10 Gyrs ago, and more than 90% were formed $>6$ Gyrs ago. The two types of galaxies show similarly flat profiles in a variety of stellar population parameters: old stellar ages indicated by $D4000$ (the spectral break at around 4000AA), high stellar metallicities, large Mgb/Fe ratios indicating fast formation, and little stellar dust attenuation. In contrast, although blue spirals also formed their central regions $>$10 Gyrs ago, both their central regions and outer disks continuously form stars over a long timescale. Our results imply that, massive red spirals are likely to share some common processes of formation (and possibly quenching) with massive red ellipticals in the sense that both types were formed at $z > 2$ through a fast formation process.Possible mechanisms for the formation and quenching of massive red spirals are discussed.
The emergence of passive galaxies in the early Universe results from the interplay among the processes responsible for their rapid assembly and for the abrupt shut-down of their SF. Investigating the individual properties and demographics of early passive galaxies will improve our understanding of these mechanisms. In this work we present a follow-up analysis of the z>3 passive galaxy candidates selected by Merlin et al. (2019) in the CANDELS fields. We begin by first confirming the accuracy of their passive classification by exploiting their sub-mm emission to demonstrate the lack of ongoing SF. Using archival ALMA observations we are able to confirm at least 61% of the observed candidates as passive. While the remainder lack sufficiently deep data for confirmation, we are able to validate the entire sample in a statistical sense. We then estimate the Stellar Mass Function (SMF) of all 101 passive candidates in three redshift bins from z=5 to z=3. We adopt a stepwise approach that has the advantage of taking into account photometric errors, observational incompleteness, and the Eddington bias without any a-posteriori correction. We observe a pronounced evolution in the SMF around z~4, indicating that we are witnessing the emergence of the passive population at this epoch. Massive (M>10^11Msun) passive galaxies, only accounting for a small (<10%) fraction of galaxies at z>4, become dominant at later epochs. Thanks to a combination of photometric quality, sample selection and methodology, we overall find a higher density of passive galaxies than previous works. The comparison with theoretical predictions, despite a qualitative agreement, denotes a still incomplete understanding of the physical processes responsible for the formation of these galaxies. Finally, we extrapolate our results to predict the number of early passive galaxies expected in surveys carried out with future facilities.
Local massive early-type galaxies are believed to have completed most of their star formation $sim10$Gyr ago and evolved without having substantial star formation since. If so, their progenitors should have roughly solar stellar metallicities ($Z_*$), comparable to their values today. We report the discovery of two lensed massive ($log M_*/M_odotsim11$), $zsim2.2$ dead galaxies, that appear markedly metal deficient given this scenario. Using 17-band $HST$+$K_{s}$+$Spitzer$ photometry and deep $HST$ grism spectra from the GLASS and SN Refsdal follow-up campaigns covering features near $lambda_{rm rest}sim4000$AA, we find these systems to be dominated by A-type stars with $log Z_*/Z_odot=-0.40pm0.02$ and $-0.49pm0.03$ ($30$-$40%$ solar) under standard assumptions. The second systems lower metallicity is robust to isochrone changes, though this choice can drive the first systems from $log Z_*/Z_odot=-0.6$ to 0.1. If these two galaxies are representative of larger samples, this finding suggests that evolutionary paths other than dry minor-merging are required for these massive galaxies. Future analyses with direct metallicity measurements-e.g., by the $James Webb Space Telescope$-will provide critical insight into the nature of such phenomena.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
