Star formation indicators and line equivalent width in Lyα galaxies

We determined temperatures and Lithium 6707 A resonance line equivalent width of a sample of 62 T Tauri stars. Lithium abundances were then estimated by using a grid of curves of growth. The lithium abundance is shown to decrease with the distance of the stars to the nearest dense core of a molecular cloud. This effect is interpreted as being due to the ages of the stars, the youngest ones being closer to still active star formation regions.

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Correlations between H α equivalent width and galaxy properties at z = 0.47: Physical or selection-driven?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab778 ◽

2021 ◽

Vol 503 (4) ◽

pp. 5115-5133

Author(s):

A A Khostovan ◽

S Malhotra ◽

J E Rhoads ◽

S Harish ◽

C Jiang ◽

...

Keyword(s):

Star Formation ◽

Equivalent Width ◽

Luminosity Function ◽

Mass Function ◽

Stellar Mass ◽

High Mass ◽

Selection Effects ◽

Star Formation Activity ◽

Low Mass ◽

Stellar Masses

ABSTRACT The H α equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic, bursty star-formation activity. Previous assessments show that the H α EW strongly anticorrelates with stellar mass as M−0.25 similar to the sSFR – stellar mass relation. However, such a correlation could be driven or even formed by selection effects. In this study, we investigate how H α EW distributions correlate with physical properties of galaxies and how selection biases could alter such correlations using a z = 0.47 narrow-band-selected sample of 1572 H α emitters from the Ly α Galaxies in the Epoch of Reionization (LAGER) survey as our observational case study. The sample covers a 3 deg2 area of COSMOS with a survey comoving volume of 1.1 × 105 Mpc3. We assume an intrinsic EW distribution to form mock samples of H α emitters and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find that H α EW intrinsically correlates with stellar mass as W0∝M−0.16 ± 0.03 and decreases by a factor of ∼3 from 107 M⊙ to 1010 M⊙, while not correcting for selection effects steepens the correlation as M−0.25 ± 0.04. We find low-mass H α emitters to be ∼320 times more likely to have rest-frame EW>200 Å compared to high-mass H α emitters. Combining the intrinsic W0–stellar mass correlation with an observed stellar mass function correctly reproduces the observed H α luminosity function, while not correcting for selection effects underestimates the number of bright emitters. This suggests that the W0–stellar mass correlation when corrected for selection effects is physically significant and reproduces three statistical distributions of galaxy populations (line luminosity function, stellar mass function, EW distribution). At lower stellar masses, we find there are more high-EW outliers compared to high stellar masses, even after we take into account selection effects. Our results suggest that high sSFR outliers indicative of bursty star formation activity are intrinsically more prevalent in low-mass H α emitters and not a byproduct of selection effects.

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Which Galaxy Property Best Predicts Quiescence?

Proceedings of the International Astronomical Union ◽

10.1017/s174392131300464x ◽

2012 ◽

Vol 8 (S295) ◽

pp. 177-177

Author(s):

Joel Leja ◽

Pieter van Dokkum ◽

Keyword(s):

Spatial Distribution ◽

Star Formation ◽

Velocity Dispersion ◽

High Redshift ◽

Line Emission ◽

Elliptical Galaxies ◽

High Dispersion ◽

Quenching Mechanism ◽

Line Flux ◽

Line Equivalent Width

AbstractIt is generally accepted that local elliptical galaxies assembled most of their mass in a burst of star formation between 1 < z < 3, yet today, their star formation has been almost entirely quenched. In order to constrain this quenching mechanism, we measure Hα line emission in galaxies sorted by multiple galaxy properties as a function of redshift to what galaxy parameter best predicts quiescence. This is done for samples of the most massive, most luminous, and galaxies with the highest velocity dispersion both locally (0.05 < z < 0.07 in the SDSS) and at high redshift (0.7 < z < 1.5 in 3D-HST). It is demonstrated through spectral stacking that velocity dispersion results in the lowest Hα line equivalent width both locally and at high redshift. The spatial distribution of the emission line flux is available from grism spectroscopy: the line flux from the high dispersion stack is centrally peaked and thus likely associated with AGN activity rather than star formation, strengthening this conclusion. Since velocity dispersion may also be the best predictor of halo mass (Wake et al. 2012), this may imply that the quenching mechanism is directly related to halo mass.

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Extinction in the 11.2 µm PAH band and the low L11.2/LIR in ULIRGs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2282 ◽

2020 ◽

Vol 497 (4) ◽

pp. 4614-4625

Author(s):

Antonio Hernán-Caballero ◽

Henrik W W Spoon ◽

Almudena Alonso-Herrero ◽

Evanthia Hatziminaoglou ◽

Georgios E Magdis ◽

...

Keyword(s):

Star Formation ◽

Equivalent Width ◽

Flux Ratio ◽

Width Ratio ◽

Galactic Centre ◽

Star Forming ◽

Intrinsic Flux ◽

Star Formation In Galaxies ◽

The Impact ◽

Small Dispersion

ABSTRACT We present a method for recovering the intrinsic (extinction-corrected) luminosity of the 11.2 μm PAH band in galaxy spectra. Using 105 high S/N Spitzer/IRS spectra of star-forming galaxies, we show that the equivalent width ratio of the 12.7 and 11.2 μm PAH bands is independent on the optical depth (τ), with small dispersion (∼5 per cent) indicative of a nearly constant intrinsic flux ratio Rint = (f12.7/f11.2)int = 0.377 ± 0.020. Conversely, the observed flux ratio, Robs = (f12.7/f11.2)obs, strongly correlates with the silicate strength (Ssil) confirming that differences in Robs reflect variation in τ. The relation between Robs and Ssil reproduces predictions for the Galactic Centre extinction law but disagrees with other laws. We calibrate the total extinction affecting the 11.2 μm PAH from Robs, which we apply to another sample of 215 galaxies with accurate measurements of the total infrared luminosity (LIR) to investigate the impact of extinction on L11.2/LIR. Correlation between L11.2/LIR and Robs independently on LIR suggests that increased extinction explains the well-known decrease in the average L11.2/LIR at high LIR. The extinction-corrected L11.2 is proportional to LIR in the range LIR = 109–1013 L⊙. These results consolidate L11.2 as a robust tracer of star formation in galaxies.

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The OTELO survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833295 ◽

2019 ◽

Vol 631 ◽

pp. A10 ◽

Cited By ~ 5

Author(s):

Marina Ramón-Pérez ◽

Ángel Bongiovanni ◽

Ana María Pérez García ◽

Jordi Cepa ◽

Maritza A. Lara-López ◽

...

Keyword(s):

Star Formation ◽

Equivalent Width ◽

Luminosity Function ◽

Star Formation Rate ◽

Formation Rate ◽

Emission Lines ◽

Different Types

Aims. We take advantage of the capability of the OTELO survey to obtain the Hα luminosity function (LF) at z ∼ 0.40. Because of the deepest coverage of OTELO, we are able to determine the faint end of the LF, and thus better constrain the star formation rate and the number of galaxies at low luminosities. The AGN contribution to this LF is estimated as well. Methods. We make use of the multiwavelength catalogue of objects in the field compiled by the OTELO survey, which is unique in terms of minimum flux and equivalent width. We also take advantage of the pseudo-spectra built for each source, which allow the identification of emission lines and the discrimination of different types of objects. Results. The Hα luminosity function at z ∼ 0.40 is obtained, which extends the current faint end by almost 1 dex, reaching minimal luminosities of log10Llim = 38.5 erg s−1 (or ∼0.002 M⊙ yr−1). The AGN contribution to the total Hα luminosity is estimated. We find that no AGN should be expected below a luminosity of log10L = 38.6 erg s−1. From the sample of non-AGN (presumably, pure SFG) at z ∼ 0.40 we estimated a star formation rate density of ρSFR = 0.012 ± 0.005 M⊙ yr−1 Mpc−3.

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H i-MaNGA: tracing the physics of the neutral and ionized ISM with the second data release

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab566 ◽

2021 ◽

Vol 503 (1) ◽

pp. 1345-1366

Author(s):

David V Stark ◽

Karen L Masters ◽

Vladimir Avila-Reese ◽

Rogemar Riffel ◽

Rogerio Riffel ◽

...

Keyword(s):

Star Formation ◽

Gas Phase ◽

Equivalent Width ◽

Surface Brightness ◽

Formation Rate ◽

Optical Emission ◽

All Optical ◽

Data Release ◽

Green Bank Telescope

ABSTRACT We present the second data release for the H i-MaNGA programme of H i follow-up observations for the SDSS-IV MaNGA survey. This release contains measurements for 3669 unique galaxies, combining 2108 Green Bank Telescope observations with an updated crossmatch of the MaNGA sample with the ALFALFA survey. We combine these data with MaNGA spectroscopic measurements to examine relationships between H i-to-stellar mass ratio (${\rm M_{H\, {\small I}}/{M_*}}$) and average ISM/star formation properties probed by optical emission lines. ${\rm M_{H\, {\small I}}/{M_*}}$ is very weakly correlated with the equivalent width of H α, implying a loose connection between the instantaneous star formation rate and the H i reservoir, although the link between ${\rm M_{H\, {\small I}}/{M_*}}$ and star formation strengthens when averaged even over only moderate time-scales (∼30 Myr). Galaxies with elevated H i depletion times have enhanced [O i]/H α and depressed H α surface brightness, consistent with more H i residing in a diffuse and/or shock-heated phase that is less capable of condensing into molecular clouds. Of all optical lines, ${\rm M_{H\, {\small I}}/{M_*}}$ correlates most strongly with oxygen equivalent width, EW(O), which is likely a result of the existing correlation between ${\rm M_{H\, {\small I}}/{M_*}}$ and gas-phase metallicity. Residuals in the ${\rm M_{H\, {\small I}}/{M_*}}$−EW(O) relation are again correlated with [O i]/H α and H α surface brightness, suggesting they are also driven by variations in the fraction of diffuse and/or shock-heated gas. We recover the strong anticorrelation between ${\rm M_{H\, {\small I}}/{M_*}}$ and gas-phase metallicity seen in previous studies. We also find a relationship between ${\rm M_{H\, {\small I}}/{M_*}}$ and [O i]6302/H α, suggesting that higher fractions of diffuse and/or shock-heated gas are more prevalent in gas-rich galaxies.

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The [O iii]+H β equivalent width distribution at z ≃ 7: implications for the contribution of galaxies to reionization

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3370 ◽

2020 ◽

Vol 500 (4) ◽

pp. 5229-5248

Author(s):

Ryan Endsley ◽

Daniel P Stark ◽

Jacopo Chevallard ◽

Stéphane Charlot

Keyword(s):

Star Formation ◽

Standard Deviation ◽

Equivalent Width ◽

Production Efficiency ◽

Massive Star ◽

Star Clusters ◽

Strong Variation ◽

Star Forming ◽

Width Distribution ◽

Intense Star Formation

ABSTRACT We quantify the distribution of [O iii]+H β line strengths at z ≃ 7 using a sample of 20 bright ($\mathrm{M}_{\mathrm{UV}}^{}$ ≲ –21) galaxies. We select these systems over wide-area fields (2.3 deg2 total) using a new colour-selection that precisely selects galaxies at z ≃ 6.63–6.83, a redshift range where blue Spitzer/IRAC [3.6]−[4.5] colours unambiguously indicate strong [O iii]+H β emission. These 20 galaxies suggest a lognormal [O iii]+H β EW distribution with median EW = 759$^{+112}_{-113}$ Å and standard deviation = 0.26$^{+0.06}_{-0.05}$ dex. We find no evidence for strong variation in this EW distribution with UV luminosity. The typical [O iii]+H β EW at z ≃ 7 implied by our sample is considerably larger than that in massive star-forming galaxies at z ≃ 2, consistent with a shift towards larger average sSFR (4.4 Gyr−1) and lower metallicities (0.16 Z⊙). We also find evidence for the emergence of a population with yet more extreme nebular emission ([O iii]+H β EW > 1200 Å) that is rarely seen at lower redshifts. These objects have extremely large sSFR (>30 Gyr−1), as would be expected for systems undergoing a burst or upturn in star formation. While this may be a short-lived phase, our results suggest that 20 per cent of the z ≃ 7 population has such extreme nebular emission, implying that galaxies likely undergo intense star formation episodes regularly at z > 6. We argue that this population may be among the most effective ionizing agents in the reionization era, both in terms of photon production efficiency and escape fraction. We furthermore suggest that galaxies passing through this large sSFR phase are likely to be very efficient in forming bound star clusters.

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Diffuse star-forming galaxies: thermal emission in radio continuum at 1.4 GHz

Bulletin of Taras Shevchenko National University of Kyiv Astronomy ◽

10.17721/btsnua.2018.58.21-23 ◽

2018 ◽

pp. 21-23

Author(s):

S. Parnovsky ◽

I. Izotova

Keyword(s):

Star Formation ◽

Radio Emission ◽

Emission Line ◽

Equivalent Width ◽

Colour Index ◽

Thermal Component ◽

Active Star ◽

Star Forming ◽

Active Star Formation ◽

Thermal Radio Emission

We determine the fraction of thermal radio emission in the total flux at the frequency of 1.4 GHz in 30 diffuse star-forming galaxies using the approach described in the paper by Parnovsky and Izotova (Astronomische Nachrichten, 2015 Vol.336, Issue 3, p.276). We use the sample of diffuse galaxies with active star formation selected from the Data Release 12 (DR12) of the Sloan Digital Sky Survey (SDSS). The SDSS spectroscopic data for diffuse galaxies were supplemented by radio data from the FIRST and NVSS catalogues. From the fluxes in the Hβ emission line corrected for extinction and aperture we estimate the fluxes of thermal component of the radio emission at the 1.4 GHz using the result of the paper by J. Caplan and L. Deharveng (Astron. Astrophys. 1986, V. 155, P.297) and compare them with total fluxes from the FIRST and NVSS. In the sample of diffuse galaxies with active star formation, the distribution of the fraction of thermal radio emission A is similar to the lognormal one with the median value of 6 %. This is less than the median value which was derived earlier by Parnovsky and Izotova for a sample of compact star-forming galaxies, but both distributions of A are similar. We study the dependence of A on the W equivalent width of the Hβ emission line and on the I colour index g-r. The fraction of thermal component increases with increasing of the equivalent width of the Hβ emission line if a colour index is constant or an increasing of the colour index at a fixed equivalent width W.

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Equivalent width Measurements in Optical Spectra of Galaxies in Local Clusters: Hints On the Star Formation History in Clusters

Open Astronomy ◽

10.1515/astro-2017-0315 ◽

2011 ◽

Vol 20 (3) ◽

pp. 435-441

Author(s):

Jacopo Fritz ◽

Bianca M. Poggianti ◽

Antonio Cava ◽

Alessia Moretti

Keyword(s):

Star Formation ◽

Equivalent Width ◽

Good Accuracy ◽

Optical Spectra ◽

Classification Criteria ◽

Spectral Lines ◽

Star Formation History ◽

Star Forming ◽

Formation History ◽

Width Measurements

Abstract Equivalent widths of spectral lines in the optical spectra of galaxies are commonly used to characterize their stellar populations and to get some insight on their evolution. Here we describe a new method to measure automatically equivalent widths of spectral lines with a good accuracy. This makes possible to classify galaxies according to the presence/absence and intensity of [O II] and Hδ lines. Based on these classification criteria, we give a description of the characteristics of the star-forming and post-starburst galaxies in local clusters, and their dependence on the cluster characteristics.

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A Decoupled Nucleus in NGC 1052

Symposium - International Astronomical Union ◽

10.1017/s0074180900109519 ◽

1995 ◽

Vol 164 ◽

pp. 438-438

Author(s):

O.K. Sil'chenko

Keyword(s):

Absorption Line ◽

Spectral Range ◽

Equivalent Width ◽

Two Dimensional ◽

Ionized Gas ◽

Radial Profiles ◽

Line Equivalent Width

The central part of NGC 1052 has been observed at the prime focus of the 6m telescope with the Multi-Pupil Spectrophotometer equipped with a two-dimensional IPCS. Ninety-nine spectra over the central 14.5″x11″ are registered in the spectral range of λλ4700 – 5400 AA and are used to map ionized-gas velocities (by [OIII]λ5007) and to derive radial profiles of absorption-line equivalent width for MgIλA5175, FeIλ5270, and Hβ.

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