scholarly journals The secular evolution of M83 central bulge

2007 ◽  
Vol 3 (S245) ◽  
pp. 297-300
Author(s):  
H. Dottori ◽  
R. J. Diaz ◽  
M. P. Agüero ◽  
D. Mast ◽  
I. Rodrigues
Keyword(s):  
High Redshift ◽  
Radio Sources ◽  
Star Forming ◽  
Secular Evolution ◽  
Left Behind ◽  
Central Bulge ◽  
Optical Wavelengths ◽  
Imaging And Spectroscopy ◽  
A Chain ◽  
Strong Evaporation

AbstractThe luminosity profile of M 83 bulge can be traced by a de Vaucouleurs' law between ≈ 200 pc and ≈ 800 pc. The inner part can be fitted by a n = −1/2 Sérsic profile. Also the IR (J − K) color shows difference between the periphery and the central part of the bulge, both properties indicating the presence of a pseudobulge. Previous Gemini-S 3-D, Paβ spectroscopy of the central ≈ 5″×13″ revealed spider like diagrams indicating disk like motion around three extended masses identified respectively with the optical nucleus (ON), with the center of the bulge isophotes, similar to the CO kinematical center (KC), and with a condensation hidden at optical wavelengths (HN), coincident with the largest lobe in 10 μm emission, most probably a cannibalized satellite. Numerical simulations show that they suffer strong evaporation and they would merge engulfing also the star forming arc in few hundred Myr, increasing the mass at the kinematical center by a factor o five or more. Upper mass limit of putative Black Holes associated to ON, KC and HN are a few ten thousand to a million solar masses. GMOS+Gemini imaging and spectroscopy of a chain of radio sources has yield no optical high redshift counterparts. This radio sources are aligned with ON, neither associated to SN nor to HII regions and might point to an older similar phenomenon, which left behind a kick-off spur.

scholarly journals Secular evolution in young galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 375-375
Author(s):  
Bruce G. Elmegreen
Keyword(s):  
Angular Momentum ◽  
Milky Way ◽  
High Redshift ◽  
Thick Disk ◽  
High Dispersion ◽  
Star Forming ◽  
Secular Evolution ◽  
Disk Mass ◽  
High Fraction ◽  
Gas Fractions

AbstractYoung galaxies viewed at high redshift have high turbulent velocities, high star formation rates, high gas fractions, and chaotic structures, suggesting wild instabilities during which giant gas clumps form and make stars in their dense regions, stir other disk stars and gas, and transport angular momentum outward with a resulting net mass flow inward (e.g., Ceverino et al.2010). At z=1.5, 40% of star-forming galaxies have significant clumps (Elmegreen et al.2007; Wuyts et al.2012), and in these, 10%-20% of the stellar mass is in clumps that last ~150 Myr (Elmegreen et al.2009; Wuyts et al.2012). The thick disk and bulge in modern galaxies could form in this phase. The similarity in the α/Fe ratio (Meléndez et al.2008), K-giant abundances (Bensby et al.2010) and ages for the Milky Way bulge and thick disk suggest they formed at the same time. High dispersion gas at z ~ 1.5 can do this because it makes the young disk thick and the SF clumps big enough to drive fast secular evolution (Elmegreen et al.2006; Genzel et al.2008; Bournaud et al.2009). Local analogues might be present in dynamically young galaxies like BCDs (Elmegreen et al.2012). The high fraction of z ~ 1.5 galaxies with massive clumps suggests clump formation is a long-lived phase and that clump torques should last ~ 1 Gyr or more even if individual clumps come and go on shorter timescales. Clump formation may cease when stars finally dominate the disk mass (Cacciato et al. 2012).

Cold gas studies of a z = 2.5 protocluster

2020 ◽  
Vol 15 (S359) ◽  
pp. 136-140
Author(s):  
Minju M. Lee ◽  
Ichi Tanaka ◽  
Rohei Kawabe
Keyword(s):  
Galaxy Evolution ◽  
High Redshift ◽  
Kinematic Model ◽  
Molecular Gas ◽  
General View ◽  
Massive Galaxies ◽  
Star Forming ◽  
Gas Kinematics ◽  
Narrow Band Filter ◽  
Stellar Masses

AbstractWe present studies of a protocluster at z =2.5, an overdense region found close to a radio galaxy, 4C 23.56, using ALMA. We observed 1.1 mm continuum, two CO lines (CO (4–3) and CO (3–2)) and the lower atomic carbon line transition ([CI](3P1-3P0)) at a few kpc (0″.3-0″.9) resolution. The primary targets are 25 star-forming galaxies selected as Hα emitters (HAEs) that are identified with a narrow band filter. These are massive galaxies with stellar masses of > 1010Mʘ that are mostly on the galaxy main sequence at z =2.5. We measure the molecular gas mass from the independent gas tracers of 1.1 mm, CO (3–2) and [CI], and investigate the gas kinematics of galaxies from CO (4–3). Molecular gas masses from the different measurements are consistent with each other for detection, with a gas fraction (fgas = Mgas/(Mgas+ Mstar)) of ≃ 0.5 on average but with a caveat. On the other hand, the CO line widths of the protocluster galaxies are typically broader by ˜50% compared to field galaxies, which can be attributed to more frequent, unresolved gas-rich mergers and/or smaller sizes than field galaxies, supported by our high-resolution images and a kinematic model fit of one of the galaxies. We discuss the expected scenario of galaxy evolution in protoclusters at high redshift but future large surveys are needed to get a more general view.

scholarly journals A survey for the missing hydrogen in high-redshift radio sources

2012 ◽  
Vol 428 (3) ◽  
pp. 2053-2063 ◽  
Author(s):  
S. J. Curran ◽  
M. T. Whiting ◽  
E. M. Sadler ◽  
C. Bignell
Keyword(s):  
High Redshift ◽  
Radio Sources

scholarly journals Variability of young stellar objects in the star-forming region Pelican Nebula

2019 ◽  
Vol 627 ◽  
pp. A135 ◽  
Author(s):  
A. Bhardwaj ◽  
N. Panwar ◽  
G. J. Herczeg ◽  
W. P. Chen ◽  
H. P. Singh
Keyword(s):  
Main Sequence ◽  
T Tauri Stars ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Physical Parameters ◽  
Main Sequence Stars ◽  
Stellar Objects ◽  
Star Forming ◽  
T Tauri ◽  
Optical Wavelengths

Context. Pre-main-sequence variability characteristics can be used to probe the physical processes leading to the formation and initial evolution of both stars and planets. Aims. The photometric variability of pre-main-sequence stars is studied at optical wavelengths to explore star–disk interactions, accretion, spots, and other physical mechanisms associated with young stellar objects. Methods. We observed a field of 16′ × 16′ in the star-forming region Pelican Nebula (IC 5070) at BVRI wavelengths for 90 nights spread over one year in 2012−2013. More than 250 epochs in the VRI bands are used to identify and classify variables up to V ∼ 21 mag. Their physical association with the cluster IC 5070 is established based on the parallaxes and proper motions from the Gaia second data release (DR2). Multiwavelength photometric data are used to estimate physical parameters based on the isochrone fitting and spectral energy distributions. Results. We present a catalog of optical time-series photometry with periods, mean magnitudes, and classifications for 95 variable stars including 67 pre-main-sequence variables towards star-forming region IC 5070. The pre-main-sequence variables are further classified as candidate classical T Tauri and weak-line T Tauri stars based on their light curve variations and the locations on the color-color and color-magnitude diagrams using optical and infrared data together with Gaia DR2 astrometry. Classical T Tauri stars display variability amplitudes up to three times the maximum fluctuation in disk-free weak-line T Tauri stars, which show strong periodic variations. Short-term variability is missed in our photometry within single nights. Several classical T Tauri stars display long-lasting (≥10 days) single or multiple fading and brightening events of up to two magnitudes at optical wavelengths. The typical mass and age of the pre-main-sequence variables from the isochrone fitting and spectral energy distributions are estimated to be ≤1 M⊙ and ∼2 Myr, respectively. We do not find any correlation between the optical amplitudes or periods with the physical parameters (mass and age) of pre-main-sequence stars. Conclusions. The low-mass pre-main-sequence stars in the Pelican Nebula region display distinct variability and color trends and nearly 30% of the variables exhibit strong periodic signatures attributed to cold spot modulations. In the case of accretion bursts and extinction events, the average amplitudes are larger than one magnitude at optical wavelengths. These optical magnitude fluctuations are stable on a timescale of one year.

Spectral Modeling of Star‐forming Regions in the Ultraviolet: Stellar Metallicity Diagnostics for High‐Redshift Galaxies

2004 ◽  
Vol 615 (1) ◽  
pp. 98-117 ◽  
Author(s):  
Samantha A. Rix ◽  
Max Pettini ◽  
Claus Leitherer ◽  
Fabio Bresolin ◽  
Rolf‐Peter Kudritzki ◽  
...  
Keyword(s):  
High Redshift ◽  
Spectral Modeling ◽  
High Redshift Galaxies ◽  
Star Forming ◽  
Star Forming Regions ◽  
Redshift Galaxies

scholarly journals Populations of OB-type stars in galaxies

2010 ◽  
Vol 6 (S272) ◽  
pp. 233-241
Author(s):  
Christopher J. Evans
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Young Star ◽  
Magellanic Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
External Galaxies

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

scholarly journals Spatially resolved studies of extragalactic jets in high redshift radio galaxies

2014 ◽  
Vol 10 (S313) ◽  
pp. 231-235
Author(s):  
Leah K. Morabito ◽  
Adam Deller ◽  
J. B. R. Oonk ◽  
Huub Röttgering ◽  
George Miley
Keyword(s):  
High Redshift ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Radio Sources ◽  
Spatially Resolved ◽  
Long Baseline ◽  
Early Results ◽  
Spectrum Radio ◽  
Extragalactic Jets ◽  
Frequency Survey

AbstractThe correlation between radio spectral steepness and redshift has been successfully used to find high redshift (z ⩾ 2) radio galaxies, but the origin of this relation is unknown. The ultra-steep spectra of high-z radio sources make them ideally suited for studies with the Low Band Antenna of the new Low Frequency Array, which covers 10–80 MHz and has baselines up to about 1300 km. As part of an ongoing survey, we use the longest baselines to map the low-frequency (< 70 MHz) spatial distributions along the jets of 5 bright extended steep spectrum high-z radio sources. From this, we will determine whether the spectra change over these spatially resolved sources, thereby constraining particle acceleration processes. We present early results from our low-frequency survey of ultra-steep spectrum radio galaxies. The first low frequency long baseline images of these objects are presented.

scholarly journals Exploration of the high-redshift universe enabled by THESEUS

2021 ◽  
Author(s):  
N. R. Tanvir ◽  
E. Le Floc’h ◽  
L. Christensen ◽  
J. Caruana ◽  
R. Salvaterra ◽  
...  
Keyword(s):  
Star Formation ◽  
Gamma Ray ◽  
High Redshift ◽  
Formation Rate ◽  
Star Forming ◽  
Chemical Enrichment ◽  
Long Duration ◽  
Absorption Studies ◽  
Population Iii Stars ◽  
High Redshift Universe

AbstractAt peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer of star formation and star-forming galaxies over the whole of cosmic history. Their bright power-law afterglows provide ideal backlights for absorption studies of the interstellar and intergalactic medium back to the reionization era. The proposed THESEUS mission is designed to detect large samples of GRBs at z > 6 in the 2030s, at a time when supporting observations with major next generation facilities will be possible, thus enabling a range of transformative science. THESEUS will allow us to explore the faint end of the luminosity function of galaxies and the star formation rate density to high redshifts; constrain the progress of re-ionisation beyond $z\gtrsim 6$ z ≳ 6 ; study in detail early chemical enrichment from stellar explosions, including signatures of Population III stars; and potentially characterize the dark energy equation of state at the highest redshifts.

scholarly journals VLBA+GBT observations of the COSMOS field and radio source counts at 1.4 GHz

2018 ◽  
Vol 616 ◽  
pp. A128 ◽  
Author(s):  
N. Herrera Ruiz ◽  
E. Middelberg ◽  
A. Deller ◽  
V. Smolčić ◽  
R. P. Norris ◽  
...  
Keyword(s):  
Radio Source ◽  
Flux Density ◽  
Lower Limit ◽  
High Sensitivity ◽  
Host Galaxy ◽  
Radio Sources ◽  
Source Population ◽  
Star Forming ◽  
Brightness Temperatures ◽  
Long Baseline

We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of μJy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, meaning that it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z ≥ 0.1). On the other hand, this technique only allows us to positively identify when a radio-active AGN is present, in other words, we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, ten of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the samples of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of >40−75% at flux density levels between 150 μJy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.

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