Epoch Of First Star Formation Research Articles

Direct Observational Evidence of Multi-epoch Massive Star Formation in G24.47+0.49

Using new continuum and molecular line data from the Atacama Large Millimeter/submillimeter Array Three-millimeter Observations of Massive Star-forming Regions (ATOMS) survey and archival Very Large Array, 4.86 GHz data, we present direct observational evidence of hierarchical triggering relating three epochs of massive star formation in a ringlike H ii region, G24.47+0.49. We find from radio flux analysis that it is excited by a massive star(s) of spectral type O8.5V–O8V from the first epoch of star formation. The swept-up ionized ring structure shows evidence of secondary collapse, and within this ring, a burst of massive star formation is observed in different evolutionary phases, which constitutes the second epoch. ATOMS spectral line (e.g., HCO+(1–0)) observations reveal an outer concentric molecular gas ring expanding at a velocity of ∼9 km s−1, constituting the direct and unambiguous detection of an expanding molecular ring. It harbors twelve dense molecular cores with surface mass density greater than 0.05 g cm−2, a threshold typical of massive star formation. Half of them are found to be subvirial and thus in gravitational collapse making them the third epoch of potential massive star-forming sites.

The 21 cm Power Spectrum from the Cosmic Dawn: First Results from the OVRO-LWA

The 21\,cm transition of neutral hydrogen is opening an observational window into the cosmic dawn of the universe---the epoch of first star formation. We use 28\,hr of data from the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) to place upper limits on the spatial power spectrum of 21\,cm emission at $z \approx 18.4$ ($\Delta_{21} \lesssim 10^4\,\text{mK}$), and within the absorption feature reported by the EDGES experiment (Bowman et al. 2018). In the process we demonstrate the first application of the double Karhunen-Lo\`{e}ve transform for foreground filtering, and diagnose the systematic errors that are currently limiting the measurement. We also provide an updated model for the angular power spectrum of low-frequency foreground emission measured from the northern hemisphere, which can be used to refine sensitivity forecasts for next-generation experiments.

Quantum-state-selective electron recombination studies suggest enhanced abundance of primordial HeH.

The epoch of first star formation in the early Universe was dominated by simple atomic and molecular species consisting mainly of two elements: hydrogen and helium. Gaining insight into this constitutive era requires a thorough understanding of molecular reactivity under primordial conditions. We used a cryogenic ion storage ring combined with a merged electron beam to measure state-specific rate coefficients of dissociative recombination, a process by which electrons destroy molecular ions. We found a pronounced decrease of the electron recombination rates for the lowest rotational states of the helium hydride ion (HeH+), compared with previous measurements at room temperature. The reduced destruction of cold HeH+ translates into an enhanced abundance of this primordial molecule at redshifts of first star and galaxy formation.

The dark side of cosmology: dark matter and dark energy.

A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales.

PROBING THE EPOCH OF PRE-REIONIZATION BY CROSS-CORRELATING COSMIC MICROWAVE AND INFRARED BACKGROUND ANISOTROPIES

The epoch of first star formation and the state of the intergalactic medium (IGM) at that time are not directly observable with current telescopes. The radiation from those early sources is now part of the Cosmic Infrared Background (CIB) and, as these sources ionize the gas around them, the IGM plasma would produce faint temperature anisotropies in the Cosmic Microwave Background (CMB) via the thermal Sunyaev-Zeldovich (TSZ) effect. While these TSZ anisotropies are too faint to be detected, we show that the cross-correlation of maps of source-subtracted CIB fluctuations from {\it Euclid}, with suitably constructed microwave maps at different frequencies can probe the physical state of the gas during reionization and test/constrain models of the early CIB sources. We identify the frequency-combined CMB-subtracted microwave maps from space and ground-based instruments to show that they can be cross-correlated with the forthcoming all-sky {\it Euclid} CIB maps to detect the cross-power at scales $\sim 5'-60'$ with the signal/noise of up to $S/N\sim 4-8$ depending on the contribution to the Thomson optical depth during those pre-reionization epochs ($\Delta \tau\simeq 0.05$) and the temperature of IGM (up to $\sim10^4$K). Such a measurement would offer a new window to explore emergence and physical properties of these first light sources.

Forming massive black holes through stellar collapse: Observational diagnostics

AbstractMassive black holes are believed to reside in the centers of many galaxies. Their seeds, 1000–100 000 solar mass black holes are believed to have formed during the first epoch of star formation. Observations of X‐ray binaries suggest that at least some intermediate mass black holes form at lower redshifts. If so, we may be able to observe these massive collapses. These collapses are very different than normal core‐collapse supernovae, however, and observing the collapse of massive stars will require different observing strategies than those used for normal stellar collapse. Unlike supernovae, the collapse of massive stars may not produce any burst of photons and we must be more creative in observing the occurrence of such exotic “outbursts”. Here we briefly review the observational prospects of massive star collapse, focusing on the ever‐present neutrino signal (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spitzer Constraints on the z = 6.56 Galaxy Lensed by Abell 370

We report on Spitzer IRAC observations of the spectroscopically confirmed z=6.56 lensed Ly-alpha emitting source HCM 6A which was found behind the cluster Abell 370. Detection of the source at 3.6 and 4.5 microns, corresponding to rest-frame optical emission, allows us to study the stellar population of this primeval galaxy. The broadband flux density at 4.5 microns is enhanced compared to the continuum at other wavelengths, likely due to the presence of strong H-alpha in emission. The derived H-alpha line flux corresponds to a star-formation rate of around 140 M_{sun}/yr, more than an order of magnitude larger than estimates from the ultraviolet continuum and Ly-alpha emission line. The dust extinction required to explain the discrepancy is A_V of about 1 mag. The inference of dust at such high redshifts is surprising and implies that the first epoch of star-formation in this galaxy occurred at z~20.

HST/ACS observations of the old and metal-poor Sagittarius dwarf irregular galaxy

We have obtained deep color−magnitude diagrams (CMDs) of the Sagittarius dwarf irregular with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. The new diagrams show for the first time the star formation history of SagDIG. The main-sequence is traced down to mF606W � 27.5, well separated from the older He burning blue loop stars. The wide color range spanned by the blue and red super-giants is consistent with Padua evolutionary models with Z ∼ 0.0004. A well-defined red giant branch indicates that the is dominated by a stellar population older than 1 Gyr, for which we have estimated a metallicity in the range (Fe/H) = −2. 2t o−1.9 depending on the adopted reddening. The identification of several C stars on a luminous asymptotic giant branch, as well as the presence of a conspicuous red clump with an elongated structure, are indicative of an extended star formation epoch between 1 and 10 Gyr ago. Perhaps most impor- tantly, we have identified a small population of stars on a genuinely old red horizontal branch at mF606W = 25.70 ± 0.05, which sets the first epoch of star formation in SagDIG back to ∼9−10 Gyr ago. This shows that SagDIG has been able to maintain a very low mean metallicity over a 10 Gyr life time, and that all Local Group dwarf galaxies share an ancient (≥10 Gyr) initial episode of star formation. Thus, at the moment, I Zw 18 remains the only exception to this general trend, favoring the so-called young galaxy scenario where a very low metallicity is not necessarily old. However, a re-analysis of ACS observations of I Zw 18 suggests that an older RGB population may be present also in I Zw 18. In order to address the interplay between stars and Inter-Stellar Medium, we compare the distribution of atomic hydrogen with that of stellar populations of various ages. The youngest stars are found in clumps located: (i) near to, but not coincident with, the highest column densities of H , and (ii) in tails reminiscent of propagating star formation. We find, however, little correlation between stellar populations older than ∼1 Gyr and the H . In particular we fail to find any generation of stars that preferentially lie within the large H  hole. We therefore exclude the possibility that the ring-like H  distribution is the result of multiple supernova events. Alternative scenarios have to be explored for the ring-like H  morphology of SagDIG, which amongst dwarf irregular galaxies, is not unusual.

The First Stars

▪ Abstract We review recent theoretical results on the formation of the first stars in the universe, and emphasize related open questions. In particular, we discuss the initial conditions for Population III star formation, as given by variants of the cold dark matter cosmology. Numerical simulations have investigated the collapse and the fragmentation of metal-free gas, showing that the first stars were predominantly very massive. The exact determination of the stellar masses, and the precise form of the primordial initial mass function, is still hampered by our limited understanding of the accretion physics and the protostellar feedback effects. We address the importance of heavy elements in bringing about the transition from an early star formation mode dominated by massive stars to the familiar mode dominated by low-mass stars at later times. We show how complementary observations, both at high redshifts and in our local cosmic neighborhood, can be utilized to probe the first epoch of star formation.

Quasar Elemental Abundances at High Redshifts

We examine rest-frame ultraviolet spectra of 70 high-redshift quasars (z ≥ 3.5) to study the chemical enrichment history of the gas closely related to the quasars and thereby estimate the epoch of first star formation. The fluxes of several ultraviolet emission lines were investigated within the framework of the most recent photoionization models to estimate the metallicity of the gas associated with the high-redshift quasars. Standard photoionization parameters and the assumption of secondary nitrogen enrichment indicate an average abundance of Z/Z☉ 4-5 in the line-emitting gas. Assuming a timescale of τevol 0.5-0.8 Gyr for the chemical enrichment of the gas, the first major star formation for quasars with z 4 should have started at a redshift of zf 6-8, corresponding to an age of the universe of several times 108 yr (H0 = 65 km s-1 Mpc-1, ΩM = 0.3, ΩΛ = 0.7). We note that this also appears to be the era of reionization of the universe. Finally, there is some evidence for a positive luminosity-metallicity relation in this high-redshift quasar sample.

White Dwarfs in Wide Binaries and the Age of the Galaxy

We present a photometric study of wide binaries with suspected white dwarf (WD) components. These systems were initially identified on the basis of their reduced proper motions and colors by W. J. Luyten (Proper Motion Survey with the Forty-Eight Inch Schmidt Telescope [Minneapolis: Univ. Minnesota Press, 1963–]) and H. L. Giclas et al. (Lowell Proper Motion Survey, Northern Hemisphere [Flagstaff: Lowell Obs., 1971], Lowell Proper Motion Survey, Southern Hemisphere [Flagstaff: Lowell Obs., 1978]). These systems usually contain a WD and a main-sequence star; however, a few contain more than two components. We obtained BVRI CCD images for approximately 475 of the 512 systems in our sample. These systems were determined by a concurrent low-resolution spectroscopy program to contain about 325 relatively cool WDs. We use this sample to determine the WD luminosity function (WDLF) and, by inference, the minimum age of the Galaxy. The WDLF was constructed using the 1/Vmax technique (M. Schmidt, ApJ, 151, 393 [1968]), as modified by T. Oswalt & J. A. Smith (Proc. Ninth European Workshop on White Dwarfs, ed. D. Koester & K. Werner [Berlin: Springer, 1995], p. 24) to correct for sample incompleteness. Error estimates were determined using the conservative approach used by J. Liebert, C. C. Dahn, & D. G. Monet (ApJ, 332, 891 [1988]). Of the spectroscopically identified WDs, 152 met the selection and completeness criteria for our study and were included in the final sample used to derive the WDLF. Most stars will end their lives as white dwarfs, slowly radiating their stored thermal energy and cooling to invisibility. The cooling timescale, calibrated using pulsating WDs, is on the order of 10 Gyr to cool to . This cooling log (L/L ) ≈ 5 , rate is slow enough that the remnants of the first epoch of star formation in the solar neighborhood are still visible. Comparison of the observed WDLF with age-dependent WDLFs integrated numerically by M. A. Wood (Proc. Ninth European Workshop on White Dwarfs [Berlin: Springer, 1995], p. 41) suggests a lower limit age of the local Galactic disk of Gyr. Assuming a ∼1 Gyr delay between the big bang 0.9 9.7 0.8 and galaxy formation, and allowing for main-sequence evolutionary times, this minimum Galactic disk age then implies a lower limit to the age of the universe of about 11 Gyr. Newly revised ages derived from globular cluster studies (B. Chaboyer, P. Demarque, P. J. Kernan, & L. M. Krauss, ApJ, 494, 96 [1998]) and recently derived cosmological ages, corrected for Hipparcos data (M. W. Feast & R. M. Catchpole, MNRAS, 286, L1 [1997]), now agree with our age determination to within 1 j. Furthermore, our age estimate is in accord with those derived from nuclear-cosmochronology studies (e.g., C. Sneden, J. J. Cowen, D. L. Burris, & J. W. Truran, ApJ, 496, 235 [1998]) and meteoritic sample analyses (e.g., L. R. Nittler & R. Cowsik, Phys. Rev. Lett., 78, 175 [1997]). Our data show no clear observational evidence for an increase in the WDLF at crystallization, , so there is log (L/L ) ≈ 3.8 ,

Large infrared and optical color gradients in the Cartwheel ring galaxy - Evidence for the first epoch of star formation in the wake of an expanding ring

view Abstract Citations (54) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Large Infrared and Optical Color Gradients in the Cartwheel Ring Galaxy: Evidence for the First Epoch of Star Formation in the Wake of an Expanding Ring Marcum, P. M. ; Appleton, P. N. ; Higdon, J. L. Abstract Substantial near-infrared and optical color gradients have been observed within the disk of the classical ring galaxy A0035-324 (the "Cartwheel"). The slope of the radial B - V, V - K color gradient coincides with starburst color evolution predictions, indicating that the age of the disk population is a function of radius. Observations indicate that the youngest stars are on the leading edge of the outer ring, and the stellar population grows increasingly older toward the nucleus. The radial color gradient, taken together with other evidence, strongly support the collisional picture for the formation of ring galaxies. Strong IR emission observed in the outer ring appears to be directly associated with the young star-forming regions rather than an evolved stellar population. We conclude that star formation is occurring in a mainly gaseous expanding density wave and that the Cartwheel is undergoing its first epoch of star formation since its formation. Publication: The Astrophysical Journal Pub Date: November 1992 DOI: 10.1086/171902 Bibcode: 1992ApJ...399...57M Keywords: Infrared Astronomy; Ring Galaxies; Star Formation; Starburst Galaxies; Astronomical Spectroscopy; Brightness Distribution; Color; Emission Spectra; Interacting Galaxies; Near Infrared Radiation; Astrophysics; GALAXIES: PHOTOMETRY; GALAXIES: INDIVIDUAL ALPHANUMERIC: A0035-324; GALAXIES: STELLAR CONTENT; STARS: FORMATION full text sources ADS | data products SIMBAD (1) NED (1)