Modelling the UV spectrum of SDSS-III/BOSS galaxies: hints towards the detection of the UV upturn at high-<i>z</i>

Cras, Claire Le; Maraston, Claudia; Thomas, Daniel; York, Donald G.

doi:10.1093/mnras/stw1024

Cited by 27 publications

(40 citation statements)

References 59 publications

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“…In the first panel we also show the underlying C09 model showing the contribution of the purely old population, clearly demonstrating that the extra blackbody component only contributes to the UV part of the SED. The fitted blackbody component usually has a temperature between 10,000 and ∼ 21, 000K, consistent with the earlier UIT observations of Brown et al (1997) and the indices derived by Le Cras et al (2016) for massive BOSS galaxies. We plot the derived temperature vs. M r (a good proxy for stellar mass) in Fig.…”

Section: Blackbody Fittingsupporting

confidence: 88%

UV SEDs of early-type cluster galaxies: a new look at the UV upturn

Ali

Bremer

Phillipps

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Using GALEX, UVOT and optical photometry, we explore the prevalence and strength of the UV-upturn in the spectra of quiescent early type galaxies in several nearby clusters. Even for galaxies with completely passive optical colours, there is a large spread in vacuum UV colour consistent with almost all having some UV upturn component. Combining GALEX and UVOT data below 3000Å, we generate for the first time comparatively detailed UV SEDs for Coma cluster galaxies. Fitting the UV upturn component with a blackbody, twenty six of these show a range of characteristic temperatures (10000-21000K) for the UV upturn population. Assuming a single temperature to explain GALEX-optical colours could underestimate the fraction of galaxies with UV upturns and mis-classify some as systems with residual star formation. The UV upturn phenomenon is not an exclusive feature found only in giant galaxies; we identify galaxies with similar (or even bluer) FUV −V colours to the giants with upturns over a range of fainter luminosities. The temperature and strength of the UV upturn are correlated with galaxy mass. Under the plausible hypothesis that the sources of the UV upturn are blue horizontal branch stars, the most likely mechanism for this is the presence of a substantial (between 4% and 20%) Helium rich (Y > 0.3) population of stars in these galaxies, potentially formed at z ∼ 4 and certainly at z > 2; this plausibly sets a lower limit of ∼ 0.3 − 0.8 × 10 10 M to the in situ stellar mass of ∼ L * galaxies at this redshift.

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Section: Blackbody Fittingsupporting

confidence: 88%

UV SEDs of early-type cluster galaxies: a new look at the UV upturn

Ali

Bremer

Phillipps

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…In this case, a pure old SSP is a good first approximation for a galaxy whose mass is larger than 10 && M ⨀ , such as the stacked spectra analysed here. However, as shown in Figure 1 and Extended Data Figure 4, the NUV data clearly indicates the inability of an old SSP to fully describe the SFH of massive ETGs, and calls for an additional component 3,14 to be fitted. This component needs to be a very hot stellar population responsible for the decrease of NUV absorption features possibly due to young stars.…”

Section: Methodsmentioning

confidence: 99%

“…We used the version of E-MILES that extends down to 6.3 Myr 40 and employ the Padova isochrones 41 . The grid of models spans metallicities, -2.32 ≤ [M/H] ≤ +0.22, with ages ranging from 6.3 Myr to 14 Gyr. We adopt a low-mass tapered bimodal initial mass function with logarithmic slope of 1.3, and scaled-solar abundances 42 .…”

Section: Methodsmentioning

confidence: 99%

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Sub one per cent mass fractions of young stars in red massive galaxies

et al. 2019

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Early-type galaxies are considered to be the endproducts of massive galaxy formation 1 . Optical spectroscopic studies reveal that massive early-type galaxies formed the bulk of their stars over short timescales (≤1 Gyr) and at high redshift (z≤2), followed by passive evolution to the present 2 . However, their optical spectra are insensitive to constrain small episodes of recent star formation, since they are dominated by old stars. Fortunately, this problem can be tackled in the ultraviolet range. While recent studies that make use of ultraviolet absorption lines have suggested the presence of young stars in a few early-type galaxies 3 , the age and mass fractions of young stars and their dependence on galaxy mass, is unknown. Here we report a detailed study of these young stellar populations, from high-quality stacked spectra of 28,663 galaxies from the BOSS survey 4 , analysing optical and ultraviolet absorption lines simultaneously. We find that residual star formation is ubiquitous in massive early-type galaxies, measuring average mass fractions of ~0.5% in young stars in the last 2 Gyr of their evolution. This fraction shows a decreasing trend with galaxy stellar mass, consistent with a down-sizing scenario 5 . We also find that synthetic galaxies from stateof-the-art cosmological numerical simulations 6 significantly overproduce both intermediate and young stellar populations. Therefore, our results pose stringent constraints on numerical simulations of galaxy formation 6,7 . Stephano Charlot for kindly providing us their new version of stellar population models extended to the UV spectral range in order to test how results change when using other SSP models.

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“…Our data to z = 0.55 are broadly consistent with previous work by Brown et al (1998bBrown et al ( , 2000aBrown et al ( , 2003 on the brightest galaxies in clusters in the sense that both sets of studies detect upturns in cluster populations out to this redshift. Le Cras et al (2016) use a series of indices (developed by Fanelli et al 1992) to measure the strength of the hot HB population in BOSS Luminous Red Galaxies and show evidence for a decline in the upturn strength at z > 0.6, though with a subset of the most massive galaxies showing an upturn even at z = 1. A caveat on this is that some of the indices used in their work also have some sensitivity to star formation, and Roseboom et al (2006) has shown that there is a large fraction of post-starburst galaxies in the LRG sample.…”

Section: Helium Rich Stars As the Source Of The Uv Upturnmentioning

confidence: 99%

The rise and fall of the UV upturn: z = 0.3, 0.55, and 0.7

Ali¹,

Bremer

Phillipps

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We have analysed the strength of the UV upturn in red sequence galaxies with luminosities reaching to below the L * point within four clusters at z = 0.3, 0.55 & 0.7. We find that the incidence and strength of the upturn remains constant up to z = 0.55. In comparison, the prevalence and strength of the UV upturn is significantly diminished in the z = 0.7 cluster, implying that the stellar population responsible for the upturn in a typical red sequence galaxy is only just developing at this redshift and is essentially fully-developed by ∼ 1 Gyr later. Of all the mainstream models that seek to explain the UV upturn phenomenon, it is those that generate the upturn through the presence of a Helium-enhanced stellar subpopulation on the (hot) horizontal branch that are most consistent with this behaviour. The epoch (z = 0.7) where the stars responsible for the upturn first evolve from the red giant branch places constraints on their age and chemical abundances. By comparing our results with the prediction made by the YEPS Helium-enhanced spectrophotometic models, we find that a solar metallicity sub-population that displays a consistent upturn between 0 < z < 0.55 but then fades by z = 0.7 would require a Helium abundance of Y 0.45, if formed at z f ∼ 4. Later formation redshifts and/or higher metallicity would further increase the Helium enhancement required to produce the observed upturn in these clusters and vice versa.

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Modelling the UV spectrum of SDSS-III/BOSS galaxies: hints towards the detection of the UV upturn at high-z

Cited by 27 publications

References 59 publications

UV SEDs of early-type cluster galaxies: a new look at the UV upturn

UV SEDs of early-type cluster galaxies: a new look at the UV upturn

Sub one per cent mass fractions of young stars in red massive galaxies

The rise and fall of the UV upturn: z = 0.3, 0.55, and 0.7

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