The build-up of pseudo-bulges in a hierarchical universe

ABSTRACT We study the cosmological build-up of pseudo-bulges using the L-Galaxies semi-analytical model for galaxy formation with a new approach for following separately the assembly of classical bulges and pseudo-bulges. Classical bulges are assumed to be the result of violent processes (i.e. mergers and starbursts), while the formation of pseudo-bulges is connected to the secular growth of discs. We apply the model to both the Millennium and the Millennium II simulations, in order to study our results across a wide range of stellar masses ($\rm 10^{7}\!-\!10^{11.5}\, {\rm M}_{\odot }$). We find that z = 0 pseudo-bulges mainly reside in galaxies of $\mathit{ M}_{\rm stellar} \, {\sim }\, 10^{10}\!-\!10^{10.5}\, {\rm M}_{\odot }$ ($\mathit{ M}_{\rm halo} \, {\sim }\, 10^{11.5}\!-\!10^{12}\, {\rm M}_{\odot }$) and we recover structural properties of these objects (e.g. sizes and bulge-to-total ratios) that are in good agreement with observational results. Tracing their formation history, we find that pseudo-bulges assembled in galaxies with a very quiet merger history, as opposed to the host galaxies of classical bulges. Regarding the bulge structure, we find that $\, {\sim }\, 30{{\ \rm per\ cent}}$ of the galaxies with a predominant pseudo-bulge feature a composite structure, hosting both a pseudo- and a classical bulge component. The classical component typically constitutes ${\sim }\, 10{{\ \rm per\ cent}}$ of the total bulge galaxy mass. When looking at the properties of the host galaxies, we find that z = 0 pseudo-bulges are hosted by main-sequence galaxies, characterized by a stellar population which is generally younger compared to the one of the hosts of classical bulges.

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DISSECTING GALAXY FORMATION MODELS WITH SENSITIVITY ANALYSIS—A NEW APPROACH TO CONSTRAIN THE MILKY WAY FORMATION HISTORY

The Astrophysical Journal ◽

10.1088/0004-637x/787/1/20 ◽

2014 ◽

Vol 787 (1) ◽

pp. 20 ◽

Cited By ~ 16

Author(s):

Facundo A. Gómez ◽

Christopher E. Coleman-Smith ◽

Brian W. O'Shea ◽

Jason Tumlinson ◽

Robert L. Wolpert

Keyword(s):

Sensitivity Analysis ◽

Galaxy Formation ◽

Milky Way ◽

New Approach ◽

Formation History

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A redshift-dependent IRX–β dust attenuation relation for TNG50 galaxies

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1900 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4773-4794 ◽

Cited By ~ 1

Author(s):

Sebastian Schulz ◽

Gergö Popping ◽

Annalisa Pillepich ◽

Dylan Nelson ◽

Mark Vogelsberger ◽

...

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Main Sequence ◽

Infrared Excess ◽

Star Forming ◽

Dust Composition ◽

Metal Ratio ◽

Stellar Masses ◽

Dust Attenuation ◽

Star Formation Histories

ABSTRACT We study the relation between the UV slope, β, and the ratio between the infrared- and UV luminosities (IRX) of galaxies from TNG50, the latest installment of the IllustrisTNG galaxy formation simulations. We select 7280 star-forming main-sequence (SFMS) galaxies with stellar mass ≥109 M⊙ at redshifts 0 ≤ z ≤ 4 and perform radiative transfer with skirt to model effects of interstellar medium dust on the emitted stellar light. Assuming a Milky Way dust type and a dust-to-metal ratio of 0.3, we find that TNG50 SFMS galaxies generally agree with observationally derived IRX–β relations at z ≲ 1. However, we find a redshift-dependent systematic offset with respect to empirically derived local relations, with the TNG50 IRX–β relation shifting towards lower β and steepening at higher redshifts. This is partially driven by variations in the dust-uncorrected UV slope of galaxies, due to different star formation histories of galaxies selected at different cosmic epochs; we suggest the remainder of the effect is caused by differences in the effective dust attenuation curves of galaxies as a function of redshift. We find a typical galaxy-to-galaxy variation of 0.3 dex in infrared excess (IRX) at fixed β, correlated with intrinsic galaxy properties: galaxies with higher star formation rates, star formation efficiencies, gas metallicities and stellar masses exhibit larger IRX values. We demonstrate a degeneracy between stellar age, dust geometry, and dust composition: z = 4 galaxies with a Small Magellanic Cloud dust type follow the same IRX–β relation as low-redshift galaxies with MW dust. We provide a redshift-dependent fitting function for the IRX–β relation for MW dust based on our models.

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The star formation history of the Fornax dwarf spheroidal galaxy

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310003200 ◽

2009 ◽

Vol 5 (S262) ◽

pp. 353-354

Author(s):

Enrico V. Held ◽

Eline Tolstoy ◽

Luca Rizzi ◽

Mary Cesetti ◽

Andrew A. Cole ◽

...

Keyword(s):

Star Formation ◽

Galaxy Evolution ◽

Stellar Population ◽

Main Sequence ◽

Dwarf Galaxy ◽

Star Formation History ◽

Stellar Content ◽

Formation History ◽

First Results ◽

History Of

AbstractWe present the first results of a comprehensive HST study of the star-formation history of Fornax dSph, based on WFPC2 imaging of 7 Fornax fields. Our observations reach the oldest main-sequence turnoffs, allowing us to address fundamental questions of dwarf galaxy evolution, such as the spatial variations in the stellar content, and whether the old stellar population is made up of stars formed in a very early burst or the result of a more continuous star formation.

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Spectral Energy Distributions of LIRGs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310006046 ◽

2009 ◽

Vol 5 (S267) ◽

pp. 143-143

Author(s):

Vivian U ◽

D. B. Sanders ◽

Keyword(s):

Stellar Population ◽

Spectral Energy ◽

Population Synthesis ◽

Host Galaxies ◽

Complete Sample ◽

Energy Distributions ◽

Preliminary Results ◽

Stellar Population Synthesis ◽

Continuum Data ◽

Stellar Masses

AbstractWe present preliminary results from a study of the SEDs of a complete sample of 65 LIRGs from GOALS. The spectral shapes at λ > 10μm are similar, while the largest variations occur in the NIR (L1μm5μm/L⊙ ~ 1.0–0.01) and UV (L1μm0.12μm/L⊙ ~ 2.0–0.005). Using stellar population synthesis models to fit the UV–NIR continuum data, we derive stellar masses for the host galaxies of log (M*/M⊙) ~ 10.2–11.4 with a mean of ~ 10.8.

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Stellar population of Sco OB2 revealed by Gaia DR2 data

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833994 ◽

2019 ◽

Vol 623 ◽

pp. A112 ◽

Cited By ~ 21

Author(s):

F. Damiani ◽

L. Prisinzano ◽

I. Pillitteri ◽

G. Micela ◽

S. Sciortino

Keyword(s):

Stellar Population ◽

Main Sequence ◽

Open Cluster ◽

Proper Motions ◽

Lower Mass ◽

Global Pattern ◽

Field Star ◽

Photometric Measurements ◽

Stellar Masses ◽

Gaia Dr2

Context. The Sco OB2 association is the nearest OB association, extending over approximately 2000 square degrees on the sky. Only its brightest and most massive members are already known (from HIPPARCOS) across its entire size, while studies of its lower mass population refer only to small portions of its extent. Aims. In this work we exploit the capabilities of Gaia DR2 measurements to search for Sco OB2 members across its entire size and down to the lowest stellar masses. Methods. We used both Gaia astrometric (proper motions and parallaxes) and photometric measurements (integrated photometry and colors) to select association members, using minimal assumptions derived mostly from the HIPPARCOS studies. Gaia resolves small details in both the kinematics of individual Sco OB2 subgroups and their distribution with distance from the Sun. We developed methods to explore the 3D kinematics of a stellar population covering large sky areas. Results. We find nearly 11 000 pre-main-sequence (PMS) members of Sco OB2 (with less than 3% field-star contamination), plus ∼3600 main-sequence (MS) candidate members with a larger (10–30%) field-star contamination. A higher confidence subsample of ∼9200 PMS (and ∼1340 MS) members is also selected (<1% contamination for the PMS), however this group is affected by larger (∼15%) incompleteness. We separately classify stars in compact and diffuse populations. Most members belong to one of several kinematically distinct diffuse populations, whose ensemble clearly outlines the shape of the entire association. Upper Sco is the densest region of Sco OB2. It is characterized by a complex spatial and kinematical structure and has no global pattern of motion. Other dense subclusters are found in Lower Centaurus-Crux and in Upper Centaurus-Lupus; the richest example of the latter, which has been recently identified, is coincident with the group near V1062 Sco. Most of the clustered stars appear to be younger than the diffuse PMS population, suggesting star formation in small groups that rapidly disperse and are diluted, reaching space densities lower than field stars while keeping memory of their original kinematics. We also find that the open cluster IC 2602 has a similar dynamics to Sco OB2, and its PMS members are currently evaporating and forming a diffuse (size ∼10°) halo around its double-peaked core.

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Star formation history and metallicity in the Galactic inner bulge revealed by the red giant branch bump

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833518 ◽

2018 ◽

Vol 620 ◽

pp. A83 ◽

Cited By ~ 16

Author(s):

F. Nogueras-Lara ◽

R. Schödel ◽

H. Dong ◽

F. Najarro ◽

A. T. Gallego-Calvente ◽

...

Keyword(s):

Stellar Population ◽

Milky Way ◽

Angular Resolution ◽

Interstellar Extinction ◽

Star Formation History ◽

Galactic Centre ◽

Luminosity Functions ◽

Formation History ◽

Red Giant ◽

The One

Context. The study of the inner region of the Milky Way bulge is hampered by high interstellar extinction and extreme source crowding. Sensitive high angular resolution near-infrared imaging is needed to study stellar populations and their characteristics in such a dense and complex environment. Aims. We aim at investigating the stellar population in the innermost Galactic bulge, to study the star formation history in this region of the Galaxy. Methods. We used the 0.2″ angular resolution JHKs data from the GALACTICNUCLEUS survey to study the stellar population within two 8.0′×3.4′ fields, about 0.6° and 0.4° to the Galactic north of the Milky Way centre and to compare it with the one in the immediate surroundings of Sagittarius A*. We also characterise the absolute extinction and the extinction curve of the two fields. Results. The average interstellar extinction to the outer and the inner field is AKs ∼ 1.20 ± 0.08 mag and ∼1.48 ± 0.10 mag, respectively. We present Ks luminosity functions that are complete down to at least two magnitudes below the red clump (RC). We detect a feature in the luminosity functions that is fainter than the RC by 0.80 ± 0.03 and 0.79 ± 0.02 mag, respectively, in the Ks band. It runs parallel to the reddening vector. We identify the feature as the red giant branch bump. Fitting α-enhanced BaSTI luminosity functions to our data, we find that a single old stellar population of ∼12.8 ± 0.6 Gyr and Z = 0.040 ± 0.003 provides the best fit. Our findings thus show that the stellar population in the innermost bulge is old, similar to the one at larger distances from the Galactic plane, and that its metallicity is about twice solar at distances as short as about 60 pc from the centre of the Milky Way, similar to what is observed at about 500 pc from the Galactic Centre. Comparing the obtained metallicity with previous known values at larger latitudes (|b| > 2°), our results favour a flattening of the gradient at |b| < 2°. As a secondary result we obtain that the extinction index in the studied regions agrees within the uncertainties with our previous value of α = 2.30 ± 0.08 that was derived for the very Galactic centre.

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Star Formation History of Early-Type Galaxies with Tidal Debris in the S4G

Proceedings of the International Astronomical Union ◽

10.1017/s1743921314004906 ◽

2012 ◽

Vol 10 (H16) ◽

pp. 129-129

Author(s):

Beatriz H. F. Ramos ◽

Karín Menéndez-Delmestre ◽

Taehyun Kim ◽

Kartik Sheth ◽

Keyword(s):

Star Formation ◽

Galaxy Formation ◽

Stellar Structure ◽

Star Formation History ◽

Early Type ◽

Uv Emission ◽

Optical Images ◽

Formation History ◽

History Of ◽

Stellar Masses

AbstractLocal early-type galaxies (ETGs), despite typically being associated to old stellar populations and passive evolution, have been in some cases observed to present peculiarities in their stellar structure, like disks and shells (e.g., Kormendy et al.1997, Rix, Carollo & Freeman 1999). Moreover, it has been observed that ETGs with such tidal features may present UV emission (Rampazzo et al.2007, Salim & Rich 2010). These properties make them relevant constraints to galaxy formation models. We are analysing the structure of nearby ETGs observed in the Spitzer Survey of Stellar Structure in Galaxies (S4G; Sheth et al.2010), which comprises the largest mid-IR survey of galaxies in the local Universe. We perform a 2D GALFIT decomposition of the 3.6μm images of 146 ETGs and examine their residual images. We identify tidal features in 17% of these, suggesting that a non-negligible ETGs fraction may have experienced (after the formation of the bulk of their stellar budget) merger events that have left signatures (Canalizo et al.2007). For 6 of these peculiar ETGs, we also applied GALFIT decomposition to public GALEX/UV and SDSS/optical images. With measurements in multiple bands, we applied SED fitting techniques to estimate star formation rates (SFR) and stellar masses for the galaxies and their tidal features. We find that these 6 peculiar ETGs present masses in agreement with the population of non-peculiar ETGs. However, SFRs are higher than what has been measured for the average ETG population (Shapiro et al.2010, SDSS MPA-JHU catalog). Based on the Kaviraj (2010) relation, we find that for these peculiar ETGs the estimated age of the most recent star formation event is less than 3Gyrs. Despite this indication of recent star formation, we have not found evidence of prominent UV emission in the tidal features (Marino et al.2010). We are currently extending our work to the full sample of peculiar ETGs identified in our sample.

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Surveys of Spectroscopic Binaries at the Center for Astrophysics

International Astronomical Union Colloquium ◽

10.1017/s0252921100006199 ◽

1992 ◽

Vol 135 ◽

pp. 110-118

Author(s):

D.W. Latham

Keyword(s):

Stellar Population ◽

Main Sequence ◽

Open Clusters ◽

Spectroscopic Binaries ◽

Main Sequence Stars ◽

Eccentric Orbits ◽

Binary Formation ◽

Wide Range ◽

Formation And Evolution ◽

Better Than

Abstract For more than a decade we have been measuring stellar radial velocities with three almost identical digital speedometers on telescopes in Arizona and Massachusetts. By now we have accumulated nearly 100,000 measurements with a typical precision of better than 1 km s-1. One of the main scientific applications has been surveys of binaries in several different stellar environments, to study the frequency and orbital characteristics of binaries in a variety of stellar populations. A main goal is to confront theories of binary formation and evolution with observational results. With various collaborators we have investigated the binary populations among pre-main-sequence stars, in the Hyades and M67 open clusters, and in the Carney-Latham proper-motion sample. Thus, we have data for coeval samples of binaries covering a wide range of ages. One result is clear evidence for evolution of binary orbits. The orbital period at which there is a transition from circular to eccentric orbits gets longer for older samples of binaries, presumably due to tidal circularization. Another result is that the frequency of binaries does not seem to depend on the stellar population. Binaries are just as common among the oldest stars in the halo of our Galaxy as among the younger stars in the disk.

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Near infrared spectroscopy and star-formation histories of 3 ≤ z ≤ 4 quiescent galaxies

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833070 ◽

2018 ◽

Vol 618 ◽

pp. A85 ◽

Cited By ~ 36

Author(s):

C. Schreiber ◽

K. Glazebrook ◽

T. Nanayakkara ◽

G. G. Kacprzak ◽

I. Labbé ◽

...

Keyword(s):

Star Formation ◽

Rest Frame ◽

Stellar Population ◽

Main Sequence ◽

Near Infrared ◽

Photometric Redshifts ◽

Wide Range ◽

Order Of Magnitude ◽

Star Formation Histories ◽

Absorption Features

We present Keck–MOSFIRE H and K spectra for a sample of 24 candidate quiescent galaxies at 3 < z < 4, identified from their rest-frame UVJ colors and photometric redshifts in the ZFOURGE and 3DHST surveys. With median integration times of one hour in H and five in K, we obtain spectroscopic redshifts for half of the sample, using either Balmer absorption lines or nebular emission lines. We confirm the high accuracy of the photometric redshifts for this spectroscopically-confirmed sample, with a median |Zphot − Zspec|/(1 + Zspec) of 1.2%. Two galaxies turn out to be dusty Hα emitters at lower redshifts (z < 2.5), and these are the only two detected in the sub-mm with ALMA. High equivalent-width [O III] emission is observed in two galaxies, contributing up to 30% of the K-band flux and mimicking the UVJ colors of an old stellar population. This implies a failure rate of only 20% for the UVJ selection at these redshifts. Lastly, Balmer absorption features are identified in four galaxies, among the brightest of the sample, confirming the absence of OB stars. We then modeled the spectra and photometry of all quiescent galaxies with a wide range of star-formation histories. We find specific star-formation rates (sSFR) lower than 0.15 Gyr−1 (a factor of ten below the main sequence) for all but one galaxy, and lower than 0.01 Gyr−1 for half of the sample. These values are consistent with the observed Hβ and [O II] luminosities, and the ALMA non-detections. The implied formation histories reveal that these galaxies have quenched on average 300 Myr prior to being observed, between z = 3.5 and 5, and that half of their stars were formed by z ∼ 5.5 with a mean SFR ~ 300 M⊙ yr−1. We finally compared the UVJ selection to a selection based instead on the sSFR, as measured from the photometry. We find that galaxies a factor of ten below the main sequence are 40% more numerous than UVJ-selected quiescent galaxies, implying that the UVJ selection is pure but incomplete. Current models fail at reproducing our observations, and underestimate either the number density of quiescent galaxies by more than an order of magnitude, or the duration of their quiescence by a factor two. Overall, these results confirm the existence of an unexpected population of quiescent galaxies at z > 3, and offer the first insights on their formation histories.

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Inverse population synthesis using a dynamical basis

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310003352 ◽

2009 ◽

Vol 5 (S262) ◽

pp. 388-389

Author(s):

Juan Mateu ◽

Gladis Magris ◽

Gustavo Bruzual

Keyword(s):

Star Formation ◽

High Resolution ◽

Stellar Population ◽

Star Formation History ◽

Population Synthesis ◽

Synthesis Algorithm ◽

Inverse Population ◽

Synthetic Spectra ◽

Formation History ◽

Good Agreement

AbstractWe introduce a new inverse population synthesis algorithm (DINBAS3D) which aims to recover the star formation and metallicity histories from galactic spectra. We investigate the use of a dynamical basis of three simple stellar population spectra that is specific for each galaxy. Our goal is to recover a robust star formation history that minimizes degeneracy effects which are very common in high resolution histories methods. In this work, we detail the method and present our findings when we apply DINBAS3D to synthetic spectra with known parameters, we compare our results with similar methods and find good agreement between them.

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