Mass loss from galaxies: feeding the IGM, recycling in the IGM

As a result of internal processes or environmental effects like ram-pressure stripping or collisions, galaxies lose a significant part of their stellar and gaseous content. Whereas the impact of such stripping on galaxy evolution has been well studied, much less attention has been given to the fate of the expelled material in the intergalactic or intra cluster medium (IGM/ICM). Observational evidence exists showing that a fraction of the injected matter is actually recycled to form a new generation of galaxies, such as the Tidal Dwarf Galaxies discovered near numerous interacting systems. Using a set of multiwavelength data, we are now able to roughly analyze the processes pertaining to their formation: from an instability in the HI clouds, through the formation of molecular gas, and to the onset of star formation. This revised version was published online in September 2006 with corrections to the Cover Date.     

Dust in the IGM: pro and contra

Observations of dust grains in the intergalactic medium (IGM) allow us to study an important aspect in the evolution of galaxies. Although its existence had been previously speculated upon, direct evidence of the presence of dust in the intergalactic space has only been available recently. We discuss various issues regarding the presence of dust in the IGM—its sources, transport mechanisms from galaxies into the IGM, its effect on reddening and on cosmological studies.     

Photometrically estimating the spatially-resolved stellar mass-to-light ratios for low-redshift galaxies

The stellar mass-to-light ratio(M_*/L) of galaxies in a given wave band shows tight correlations with optical colors, which have been widely applied as cheap estimators of galaxy stellar masses. These estimators are usually calibrated using either broadband spectral energy distributions(SEDs) or spectroscopy at galactic centers. However, it is unclear whether the same estimators provide unbiased M_*/L for different regions within a galaxy. In this work we employ integral field spectroscopy from the Mapping Nearby Galaxies at Apache Point Observatory(Ma NGA) survey. We also examine the correlations of spatially resolved M_*/L obtained from full spectral fitting, with different color indices, as well as galaxy morphology types, distances to the galactic center, and stellar population parameters such as stellar age and metallicity.We find that the(g-r) color is better than any other color indices, and it provides almost unbiased M_*/L for all the SDSS five bands and for all types of galaxies or regions, with only slight biases depending on stellar age and metallicity. Our analysis indicates that combining multiple colors and/or including other properties to reduce the systematics and scatters of the estimator does not work better than a single color index defined by two bands. Therefore, we have obtained a best estimator with the(g-r) color and applied it to the Ma NGA galaxies. Both the two-dimensional map and radial profile of M_*/L are reproduced well in most cases. Our estimator may be applied to obtain surface mass density maps for large samples of galaxies from imaging surveys at both low and high redshifts.     

The low-redshift evolution of the Lyman-β forest

The low-redshift evolution of the intergalactic medium is investigated using hydrodynamic cosmological simulations. The assumed cosmological model is a critical density cold dark matter universe. The imposed uniform background of ionizing radiation has the amplitude, shape and redshift evolution as computed from the observed quasar luminosity function by Haardt &38; Madau. We have analysed simulated Lyman-α spectra using Voigt-profile fitting, mimicking the procedure with which quasar spectra are analysed. Our simulations reproduce the observed evolution of the number of Lyman-α absorption lines over the whole observed interval of z  = 0.5 to 4. In particular, our simulations show that the decrease in the rate of evolution of Lyman-α absorption lines at z  ≤ 2, as observed by the Hubble Space Telescope , can be explained by the steep decline in the photoionizing background resulting from the rapid decline in quasar numbers at low redshift.     

Feast and Famine: regulation of black hole growth in low-redshift galaxies

We analyse the observed distribution of Eddington ratios  ( L / L _Edd)  as a function of supermassive black hole mass for a large sample of nearby galaxies drawn from the Sloan Digital Sky Survey. We demonstrate that there are two distinct regimes of black hole growth in nearby galaxies. The first is associated with galaxies with significant star formation [   M _*/star formation rate (SFR) ∼  a Hubble time] in their central kiloparsec regions, and is characterized by a broad lognormal distribution of accretion rates peaked at a few per cent of the Eddington limit. In this regime, the Eddington ratio distribution is independent of the mass of the black hole and shows little dependence on the central stellar population of the galaxy. The second regime is associated with galaxies with old central stellar populations (   M _*/SFR ≫  a Hubble time), and is characterized by a power-law distribution function of Eddington ratios. In this regime, the time-averaged mass accretion rate on to black holes is proportional to the mass of stars in the galaxy bulge, with a constant of proportionality that depends on the mean stellar age of the stars. This result is once again independent of black hole mass. We show that both the slope of the power law and the decrease in the accretion rate on to black holes in old galaxies are consistent with population synthesis model predictions of the decline in stellar mass loss rates as a function of mean stellar age. Our results lead to a very simple picture of black hole growth in the local Universe. If the supply of cold gas in a galaxy bulge is plentiful, the black hole regulates its own growth at a rate that does not further depend on the properties of the interstellar medium. Once the gas runs out, black hole growth is regulated by the rate at which evolved stars lose their mass.     

The temperature of IGM at high redshifts:shock heating and high mach problem

The thermal history of cosmic gas in the dark ages remains largely unknown.It is important to quantify the impact of relevant physics on the IGM temperature between z=10 and z～30,in order to interpret recent and oncoming observations,including results reported by EDGES.We revisit the gas heating due to structure formation shocks in this era,using a set of fixed grid cosmological hydrodynamical simulations performed by three different codes.In all our simulations,the cosmic gas is predicted to be in multiphase state since z 30.The gas surrounding high density peaks gradually develops a relation more sharp than T ∝ρ~(2/3),approximately T ∝ρ~2,from z=30 to z=11,might be due to shock heating.Meanwhile,the gas in void region tends to have a large local Mach number,and their thermal state varies significantly from code to code.In the redshift range 11-20,the mass fraction of gas shock heated above the CMB temperature in our simulations is larger than previous semi-analytical results by a factor of 2 to 8.At z=15,the fraction varies from～19% to 52% among different codes.Between z=11 and z=20,the gas temperature 1/T_K_M~(-1) is predicted to be～10-20 K by two codes,much higher than the adiabatic cooling model and some previous works.However,in our simulations performed by RAMSES,1/T_K_M~(-1)is predicted to be even below the temperature required to explain result of the EDGES.Given the fact that different codes give different predictions,currently,it seems a challenge to make solid prediction on the temperature of gas at z～17 in simulations.     

Probing the neutral fraction of the IGM with GRBs during the epoch of reionization

We show that near-infrared observations of the red side of the Lyα line from a single gamma-ray burst (GRB) afterglow cannot be used to constrain the global neutral fraction of the intergalactic medium (IGM),     , at the GRB's redshift to better than     . Some GRB sightlines will encounter more neutral hydrogen than others at fixed     owing to the patchiness of reionization. GRBs during the epoch of reionization will often bear no discernible signature of a neutral IGM in their afterglow spectra. We discuss the constraints on     from the   z = 6.3  burst, GRB050904, and quantify the probability of detecting a neutral IGM using future spectroscopic observations of high-redshift, near-infrared GRB afterglows. Assuming an observation with signal-to-noise ratio similar to the Subaru FOCAS spectrum of GRB050904 and that the column density distribution of damped Lyα absorbers is the same as measured at lower redshifts, a GRB from an epoch when     can be used to detect a partly neutral IGM at 97 per cent confidence level ≈10 per cent of the time (and, for an observation with three times the sensitivity, ≈30 per cent of the time).     

The contribution of the IGM and minihaloes to the 21-cm signal of reionization

We study the statistical properties of the cosmological 21-cm signal from both the intergalactic medium (IGM) and minihaloes, using a reionization simulation that includes a self-consistent treatment of minihalo photoevaporation. We consider two models for minihalo formation and three typical thermal states of the IGM – heating purely by ionization, heating from both ionizing and Lyα photons and a maximal 'strong heating' model. We find that the signal from the IGM is almost always dominant over that from minihaloes. In our calculation, the differential brightness temperature,  δ T _b,  of minihaloes is never larger than 2 mK. Although there are indeed some differences in the signals from the minihaloes and from the IGM, even with the planned generation of radio telescopes it will be unfeasible to detect them. However, minihaloes significantly affect the ionization state of the IGM and the corresponding 21-cm flux.     

A comparison between the Hubble diagrams of type-I Seyfert galaxies and low-redshift,radio-weak quasars

We took 30 low-redshift, radio-weak quasars with 2 or more forbidden lines, and 16 Type-I Seyfert galaxies of the non-violent subtype, and compared their Hubble diagrams. We found that they each have a high correlation on the diagram, but they do not fall on a continuous line. This suggests that, contrary to the surmise by some people, they are not the same type of object. If quasars do evolve into Seyferts, then the transition must be very brief and rapid.     

Sakurai's Object: characterizing the near-infrared CO ejecta between 2003 and 2007

We present observations of Sakurai's Object obtained at 1–5 μm between 2003 and 2007. By fitting a radiative transfer model to an echelle spectrum of CO fundamental absorption features around  4.7 μm  , we determine the excitation conditions in the line-forming region. We find  ¹²C/¹³C = 3.5^+2.0_−1.5  , consistent with CO originating in ejecta processed by the very late thermal pulse, rather than in the pre-existing planetary nebula. We demonstrate the existence of  2.2 × 10⁻⁶≤ M _CO≤ 2.7 × 10⁻⁶ M_⊙  of CO ejecta outside the dust, forming a high-velocity wind of  500 ± 80 km s⁻¹  . We find evidence for significant weakening of the CO band and cooling of the dust around the central star between 2003 and 2005. The gas and dust temperatures are implausibly high for stellar radiation to be the sole contributor.     

Metal enrichment via ram pressure stripping in the IGM of the compact galaxy group RGH 80

By creating and analyzing two dimensional gas temperature and abundance maps of the RGH 80 compact galaxy group with high-quality Chandra data,we detect a high-abundance (■0.7 Z⊙) arc,where the metal abundance is significantly higher than the surrounding regions by ■0.3Z⊙.This structure shows tight spatial correlations with the member galaxy PGC 046529,as well as with the arm-like feature identified on the X-ray image in the previous work of Randall et al.(2009).Since no apparent signature of AGN activity i...     

A survey of weak stability boundaries in the Sun-Mars system

We investigate the weak stability boundary(WSB) for a new primary, Mars,in the framework of the planar circular restricted 3-body problem, and also in the planar bicircular restricted 4-body problem by including a perturbation due to Jupiter. For the sake of a simple stability/instability criterion, our computations have been done using the equations of motion in polar coordinates. It is found that the relative size of the weakly stable sets around Mars is much larger than that of the Earth-Moon and the Sun-Jupiter systems, as the mass ratio of the Sun-Mars system is significantly smaller.We propose that this difference could be scaled by the Hill radius. In an enlarged view of the domain close to Mars, the geometry of the WSB has been presented for various parameters and compared to previous works. Our results also show that Jupiter’s gravitational force would strongly affect the Martian stable regions and should be taken into account to design a ballistic capture trajectory.     

Correlation of parameters characterizing the latitudinal distribution of sunspots

We attempt to establish a correlation between the solar activity level and some characteristics of the latitude distribution of sunspots by means of center-of-latitude (COL) of observed sunspots. We calculate the COL by taking the area weighted mean latitude of sunspots for each calendar month during a cycle, and adopt the cycle-integrated sunspot area as a measure of the strength of a cycle. We first determine the latitudinal distribution of COL of sunspots. We then compute three different statistical correlations between the cycle-integrated sunspot areas and the fitting parameters of all sunspot cycles from 1878 to 2009. Our main findings are as follows: (1) The distribution of COL is bimodal well represented by a double Gaussian function. (2) Ignoring cycle 19, the characteristic width of the distribution of COL shows a significant correlation with the cycle amplitude. (3) A correlation between the location of the maxima of the COL distribution (either centroid₁ or centroid₂) and the sum of sunspot area can be found, when the data point corresponding to the solar cycle 19 is omitted.