Contribution To Luminosity Research Articles

Broad-band colours and overall photometric properties of template galaxy models from stellar population synthesis

We present here a new set of evolutionary population synthesis models for template galaxies along the Hubble morphological sequence. The models, which account for the individual evolution of the bulge, disc, and halo components, provide basic morphological features, along with bolometric luminosity and colour evolution (including Johnson/Cousins, Gunn g, r, i, and Washington C, M, T1, T2 photometric systems) between 1 and 15 Gyr. The luminosity contribution from residual gas is also evaluated, both in terms of nebular continuum and Balmer-line enhancement. Our theoretical framework relies on the observed colours of present-day galaxies, coupled with a minimal set of physical assumptions related to simple stellar population (SSP) evolution theory, to constrain the overall distinctive properties of galaxies at earlier epochs. A comparison with more elaborate photometric models, and with empirical sets of reference spectral energy distributions (SEDs) for early- and late-type galaxies is accomplished, in order to test output reliability and investigate the internal uncertainty of the models. The match with observed colours of present-day galaxies tightly constrain the stellar birth rate, b, which smoothly increases from E to Im types. The comparison with the observed supernova (SN) rate in low-redshift galaxies shows, as well, a pretty good agreement, and allows us to tune up the inferred star formation activity and the SN and hypernova rates among the different galaxy morphological types. Among others, these results could find useful application also in cosmological studies, given for instance the claimed relationship between hypernova events and gamma-ray bursts. One outstanding feature of the back-in-time evolution model is the prevailing luminosity contribution of the bulge at early epochs. As a consequence, the current morphological look of galaxies might drastically change when moving to larger distances, and we discuss here how sensibly this bias could affect the observation (and the interpretation) of high-redshift surveys. In addition to broad-band colours, the modelling of Balmer line emission in disc-dominated systems shows that striking emission lines, like Hα, can very effectively track stellar birth rate in a galaxy. For these features to be useful age tracers as well, however, one should first assess the real change of b versus time on the basis of supplementary (and physically independent) arguments.

Monitoring Chandra Observations of the Quasi-persistent Neutron Star X-Ray Transient MXB 1659-29 in Quiescence: The Cooling Curve of the Heated Neutron Star Crust

We have observed the quasi-persistent neutron-star X-ray transient and eclipsing binary MXB 1659-29 in quiescence on three occasions with Chandra. The purpose of our observations was to monitor the quiescent behavior of the source after its last prolonged (~2.5 years) outburst which ended in September 2001. The X-ray spectra of the source are consistent with thermal radiation from the neutron-star surface. We found that the bolometric flux of the source decreased by a factor of 7-9 over the time-span of 1.5 years between our first and last Chandra observations. The effective temperature also decreased, by a factor of 1.6-1.7. The decrease in time of the bolometric flux and effective temperature can be described using exponential decay functions, with e-folding times of 0.7 and ~3 years, respectively. Our results are consistent with the hypothesis that we observed a cooling neutron-star crust which was heated considerably during the prolonged accretion event and which is still out of thermal equilibrium with the neutron-star core. We could only determine upper-limits for any luminosity contribution due to the thermal state of the neutron-star core. The rapid cooling of the neutron-star crust implies that it has a large thermal conductivity. Our results also suggest that enhanced cooling processes are present in the neutron-star core.

The globular cluster system of NGC 4374

We study the globular cluster system (GCS) of the giant elliptical NGC 4374 (M 84) in the Virgo cluster using B and R photometry. The colour distribution is bimodal with peaks at B − R = 1.11 and B − R = 1.36, fitting well to those found in other early-type galaxies. The radial profile of the cluster number density is flatter than the galaxy light. Using the luminosity function we derive a distance modulus of µ = 31.61 ± 0.2, which within the uncertainty agrees with the distance from surface brightness fluctuations. Blue and red clusters show similar radial concentrations and azimuthal distributions. The total number of clusters is N = 1775 ± 150, which together with our distance modulus leads to a specific frequency of S N = 1.6 ± 0.3. This value is surprisingly low for a giant elliptical, but resembles the case of merger remnants like NGC 1316, where the low specific frequency is probably caused by the luminosity contribution of an intermediate-age population. A further common property is the high rate of type Ia supernovae which also may indicate the existence of a younger population. However, unlike in the case of NGC 1316, one cannot find any further evidence that NGC 4374 indeed hosts younger populations. The low specific frequency would also fit to a S0 galaxy seen face-on.

Wavelength and redshift dependence of bulge/total light ratios in galaxies

HST has opened the possibility to decompose the surface brightness profiles of galaxies up to significant redshifts and look-back times into r 1/4 −bulge and exponential disk components. This should allow to study the redshift evolution of bulge and disk luminosity contributions and discriminate between the different formation scenarios for these galaxy compo- nents currently discussed, i.e. decide if star formation in bulges and disks started at the same time or was delayed in either of the two components. An indispensable prerequisite for the comparison of bulge-to-disk ratios of galaxies at different redshifts is to properly account for cosmological band shift and evolutionary effects. We present evolutionary synthesis models for both components and add their spectra in various proportions to obtain the full range of local galaxies' B-band bulge-to-total light ratios. Bulge star formation is assumed to occur on a short timescale of 10 9 yr, disk star formation proceeds at a constant rate. We study the evolution of the relative light contributions of both compo- nents backward in time and, for a given cosmological model, as a function of redshift. This allows us to see how far back into the past the locally well-established correlation between galaxy morphologies and spectral properties can hold. To cope with the present uncertainty about the formation epochs of bulge and disk components we present models for three scenarios: bulges and disks of equal age, old bulges and delayed disk star formation, and old disks with subsequent bulge star formation. We quantitatively show the wavelength dependence of bulge-to-total (=B/T) light ratios for local galaxies. The different star formation timescales for bulge and disk components lead to B/T ratios that significantly increase from U through I-bands (by factors 4-6 for weak bulge systems ∼Sc) with the rate of increase slightly depending on the relative ages of the two components. The redshift evolution of B/T-ratios in various bands U, B, V, I, H is calculated accounting both for cosmological and evolu- tionary corrections assuming a standard cosmology (H0 = 65, Ω0 = 0.1, Λ0 = 0). In particular, for the two scenarios with old bulges and old or younger disks, the redshift evolution of B/T-ratios is dramatic in every band and both for galaxies ending up at z ∼ 0 with low and high B-band B/T light ratios. Our results clearly show that it does not make any sense to compare B/T ratios measured in one and the same band for galaxies at different redshifts without fully accounting for evolutionary and cosmological effects. These, unfortunately, significantly depend on the relative ages of the two components and, hence, on the galaxy formation scenario adopted. We also show that simultaneous decomposition of galaxy profiles in several bands can give direct information about these relative ages and constrain formation scenarios for the different galaxy components. Of the wavelength bands we explore (U, B, V, I, H), the I -a ndH-bands show the smoothest redshift evolution and, hence, are best suited for a first order comparison of galaxies over the redshift range from z = 0t oz > 1. Our robust result that - irrespec- tive of the respective ages of the bulge and disk stellar components - I-band B/T-ratios apparently increase with increasing redshift for all galaxy types with present B/T > 0.1 implies that the scarcity of bulge-strong systems at z ≥ 0.8 reported by Marleau & Simard (1998) and Aguerri & Trujillo (2002) for HDF and Hawaiian Deep Field galaxies is further enhanced.

Multicolor photometry of ten Seyfert 1 galaxies

We present BVI photometry of ten Seyfert 1 galaxies and narrow band H-alpha images for six of these objects as well. The results indicate that the luminosity sample distribution has an amplitude of almost 4 magnitudes with an average of M_B=-20.7. The observed morphologies are confined to early type galaxies. A barred structure is found in only 2 objects. Despite that early morphological types are dominant in this sample, integrated (B-V) colors are very blue. For instance, the SO galaxies show, on average, a (B-V)=0.78. This effect seems to be caused by the luminosity contribution of the active nucleus and/or the disk to the total luminosity of the galaxy. In the B band, the contribution of the active galactic nucleus to the total luminosity of the galaxy varies from 3% to almost 60% and the bulge to disk luminosity ratio (L_bulge/L_disk) ranges from 0.6 to 22. Signs of tidal interactions seems to be a common characteristic since they are observed in 6 of the objects and one of them seems to be located in a poor cluster not yet identified in the literature. H_alpha extended emission is rare, with only 1 galaxy showing clear evidence of it. Luminosity profile decomposition shows that the model Gauss + bulge + disk properly reproduces the surface brightness of the galaxies. However, in order to account for the luminosity profile, most of the disk galaxies needs the inner truncated exponential form with a central cutoff radius ranging from 3 to 10 kpc. This is interpreted in terms of reddened regions that are well identified in the B-V color maps. These regions present very similar colors among them, with (B-V)~1.2. This fact could be associated to the presence of dust confined in the inner regions of the galaxies.

Infrared Properties of Cataclysmic Variables in the 2 Micron All‐Sky Survey Second Incremental Data Release

Cataclysmic variables (CVs) have "traditionally" been observed primarily at short wavelengths because accretion-generated luminosity, which peaks in the optical-ultraviolet, dominates the radiated energy of most systems. Hence, relatively little is known about their infrared (IR) properties. Investigating CVs in the IR will contribute to the understanding of key system components that are expected to radiate at these wavelengths, such as the cool outer disk, accretion stream, and secondary star. We have compiled the near-IR J, H, and Ks band photometry of all cataclysmic variables contained in the sky coverage of the Second Incremental Data Release of the 2 Micron All Sky Survey (2MASS). This data comprises 251 cataclysmic variables with reliably identified near-IR counterparts and S/N > 10 photometry in one or more of the three near-IR bands. In addition to tables containing the 2MASS data, we present a set of near-IR finding charts for selected systems. A comparison between the 2MASS photometry and various literature sources of near-IR photometry of cataclysmic variables shows good agreement after allowing for differences in photometric systems and the intrinsic variability of cataclysmic variables. The bulk of our analysis consists of an exploration of near-IR color-color diagrams of the main cataclysmic variable classes. Results from this analysis include: (1) dwarf novae in outburst and quiescence occupy distinct regions of their color-color diagram; (2) nova-like CVs (and dwarf novae in outburst) have colors similar to F-K main-sequence stars, although this does not imply that they have F-K type secondary stars; (3) polars and intermediate polars also occupy distinct regions in their color-color diagram, with most polars having colors essentially indistinguishable from late (M0+) main-sequence stars; (4) there is no strong correlation between age and color for novae, except that many old novae (>75 yr since outburst) have colors similar to F-K main-sequence stars; and (5) there are unusual and unexplained loci of data points in all the color-color diagrams that warrant further investigation in the IR. Except in the case of the polars, near-IR photometry of cataclysmic variables does not isolate the luminosity contribution of their secondary stars. In general, the near-IR colors of cataclysmic variables are significantly and systematically offset blueward of the spectral type of secondary star expected at their orbital periods. This blue contamination of the near-IR light almost certainly originates from the accretion process. For a few systems, their near-IR color is redder than the secondary star expected at their orbital period. One effect that can explain some, but not all, of the red-excess cataclysmic variables is the presence of an evolved secondary star. We suggest that this can also be caused by the luminosity contribution of the cool outer regions of prominent accretion disks. There is at least a weak trend of redder color in higher inclination systems (in which the disk rim would be most visible and most obscure the hot inner region) that supports this hypothesis.

Evolutionary synthesis of stellar populations: a modular tool

A new tool for the Evolutionary Synthesis of Stellar Populations (EPS) is presented, which is based on three independent matrices, giving respectively: 1) the fuel consumption during each evolutionary phase as a function of stellar mass; 2) the typical temperatures and gravities during such phases; 3) colours and bolometric corrections as functions of gravity and temperature. The modular structure of the code allows to easily assess the impact on the synthetic spectral energy distribution of the various assumptions and model ingredients, such as, for example, uncertainties in stellar evolutionary models, mixing length, the temperature distribution of horizontal branch (HB) stars, AGB mass loss, and colour-temperature transformations. The so-called ``AGB-Phase Transition'' in Magellanic Cloud clusters is used to calibrate the contribution of the Thermally Pulsing Asymptotic Giant Branch phase (TP-AGB) to the synthetic integrated luminosity. As an illustrative example, solar metallicity ($Y=0.27,Z=0.02$) models, with ages ranging between 30 {\rm Myr} and 15 {\rm Gyr} and various choices for the slope of the Initial Mass Function (IMF), are presented. Synthetic broad band colours and the luminosity contributions of the various evolutionary stages are compared with LMC and Galactic globular cluster data. In all these cases, a good agreement is found. Finally, we show the evolution of stellar mass-to-light ratios in the bolometric and U,B,V,R, and K passbands, in which the contribution of stellar remnants is accounted for.

Contrast of faculae near the disk center and solar variability

We analyze simultaneous, or near‐simultaneous, coregistered, digital, photometric images of solar photospheric intensity and line‐of‐sight magnetic field. Images were made with the Lockheed tunable filter instrument at the Swedish Solar Observatory, La Palma, with the video spectra‐spectroheliograph system at the San Fernando Observatory and with the new NASA spectromagnetograph at the National Solar Observatory at Kitt Peak. We study the disk center contrasts of small magnetic elements. While active region faculae are dark at disk center quiet Sun network features are bright. The populations of magnetic field elements that make up these two kinds of features are quite different. Different contrast center‐limb functions must be used when estimating their irradiance or luminosity contributions. The disk center contrasts of active region faculae are color dependent and indicate a depth effect related to the H− opacity of the facular atmosphere. This result is important for calibration of monochromatic observations of faculae to bolometric irradiance fluctuations. We emphasize the value of cooperative observations among installations whose differing strengths are complementary.

The properties of X-ray-selected active galactic nuclei. I - Luminosity function, cosmological evolution, and contribution to the diffuse X-ray background

X-ray luminosity functions (XLFs) and their implications for cosmological evolution are determined for 420 X-ray-selected active galactic nuclei (AGN). The local XLFs flatten considerably when L(x) is less than or equal to 5 x 10 to the 42nd ergs/s, and higher-luminosity XLF are demonstrated to fit a power-law approximation. Cosmological evolution in terms of two pure-luminosity evolutionary models is directly supported by model-independent AGN XLF, showing weak evolution when z is less than 0.4 and more pronounced evolution at higher z. The parameter C is determined for the two models, and the values support the 'slower' evolution of these AGN relative to QSOs selected optically. The deevolved XLF best-fit slope is found to be 3.05 for high luminosities and 1.35 for low luminosities, with no evidence of slope changes for other luminosities. 38 refs.

The infrared color evolution of active nuclei

view Abstract Citations (14) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Infrared Color Evolution of Active Nuclei Baan, Willem A. Abstract The far-infrared color evolution is studied for galaxies with a nuclear starburst or an AGN. The nuclear source heats the surrounding dust to an effective blackbody temperature (T_d_ = 50-100 K). The color and luminosity evolution for such galaxies is simulated by letting the central heating source and the resulting warm dust emission (the primary source) decay exponentially in combination with a slower decaying secondary IR emission source. Secondary spectral components can be nonthermal or (hot or cold) thermal in nature and may be associated with the nuclear activity or with the rest of the galaxy. The evolving far-infrared (FIR) galaxy traverses the FIR color diagrams in a rather systematic fashion, and an FIR galaxy can be modeled very effectively with an appropriate mixture of primary and secondary luminosity contributions. The secondary components must have an initial strength of 0.1-0.005 relative to the primary source. Superluminous FIR sources with dominant nuclear sources lie at the start of the simulated evolutionary tracks in the color-color diagrams. While these sources evolve across the color diagram they will reveal more of their nuclear characteristics and eventually they may appear to the observer as normal Seyferts or quasars. The group of powerful FIR sources also incorporates the OH megamaser galaxies. A luminosity function is constructed for the family of nuclear FIR sources. A single distribution of nuclear FIR sources can account for the observed luminosity function at high L_IR_. Another distribution of nonnuclear sources is required to explain the low-luminosity end. Publication: The Astrophysical Journal Pub Date: July 1988 DOI: 10.1086/166508 Bibcode: 1988ApJ...330..743B Keywords: Active Galactic Nuclei; Color-Color Diagram; Infrared Sources (Astronomy); Seyfert Galaxies; Far Infrared Radiation; Infrared Spectra; Interstellar Matter; Luminosity; Starburst Galaxies; Astrophysics; GALAXIES: NUCLEI; INFRARED: SOURCES; INTERSTELLAR: GRAINS full text sources ADS | data products SIMBAD (10) NED (6)

Far-infrared photometry of low-mass pre-main-sequence stars with broad CO wings

A sample of 14 low-mass premain-sequence stars were studied in the far-infrared. There is evidence for outflowing material around twelve of these stars; in most cases the evidence includes broad wings on the profiles of the CO J = 2 to 1 line. Ten of the objects were detected (5 sigma) at 100 micros, and seven were mapped at 50 and 100 micros. The far-infrared emission makes a significant contribution to the total luminosity of the objects. It is found that the force available from radiation pressure is not sufficient to drive the outflows. Any process which taps the same energy source as does the present stellar luminosity must have high efficiency.

Host galaxies of quasars and their association with galaxy clusters

view Abstract Citations (146) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Host galaxies of quasars and their association with galaxy clusters. Gehren, T. ; Fried, J. ; Wehinger, P. A. ; Wyckoff, S. Abstract Seventeen quasars with redshifts ranging from 0.044 to 0.828 have been observed through an r filter using a CCD detector. Using a point-spread function defined by field stars exposed on the same CCD frame as the quasar, point-by-point subtraction of the quasar nucleus from the image reveals some of the structure in the nebulosity underlying essentially all quasars with redshifts ⪉0.5. Under the assumption that the quasar nuclei and the underlying nebulosities have the same cosmological redshifts, absolute magnitudes and metric diameters of the resolved structures again support the interpretation that quasars are central events in distant galaxies. The morphologies of the resolved galaxies underlying the quasars PHL 909, 3Cr 48, and 0241+622 are suggestive of tidal interactions with nearby companion galaxies. Counts of faint galaxies in the vicinity of the quasar images indicate that quasars are usually situated in groups or clusters of galaxies which are dominated by the luminosity contribution of the quasar host galaxy. Publication: The Astrophysical Journal Pub Date: March 1984 DOI: 10.1086/161763 Bibcode: 1984ApJ...278...11G Keywords: Galactic Clusters; Galactic Nuclei; Isophotes; Luminosity; Quasars; Red Shift; Cassegrain Optics; Charge Coupled Devices; Elliptical Galaxies; Galactic Structure; Nebulae; Spiral Galaxies; Astrophysics full text sources ADS | data products NED (17) SIMBAD (16)