We study the cosmological evolution for a universe in the presence of a continuous tower of massive scalar fields which can drive the current phase of accelerated expansion of the universe and, in addition, can contribute as a dark matter component. The tower consists of a continuous set of massive scalar fields with a gaussian mass distribution. We show that, in a certain region of the parameter space, the {\it heavy} modes of the tower (those with masses much larger than the Hubble expansion rate) dominate at early times and make the tower behave like the usual single scalar field whose coherent oscillations around the minimum of the potential give a matter-like contribution. On the other hand, at late times, the {\it light} modes (those with masses much smaller than the Hubble expansion rate) overcome the energy density of the tower and they behave like a perfect fluid with equation of state ranging from 0 to -1, depending on the spectral index of the initial spectrum. This is a distinctive feature of the tower with respect to the case of quintessence fields, since a massive scalar field can only give acceleration with equation of state close to -1. Such unique property is the result of a synergy effect between the different mass modes. Interestingly, we find that, for some choices of the spectral index, the tower tracks the matter component at high redshifts (or it can even play the role of the dark matter) and eventually become the dominant component of the universe and give rise to an accelerated expansion.
Following a first study of the central regions of M32 that illustrated the power of integral-field spectroscopy (IFS) in detecting and measuring the [O III]{\lambda}5007 emission of PNe against a strong stellar background, we turn to the very nuclear PN population of M31, within 80 pc of its centre. We show that PNe can also be found in the presence of emission from diffuse gas and further illustrate the excellent sensitivity of IFS in detecting extragalactic PNe through a comparison with narrowband images obtained with the Hubble Space Telescope. We find the nuclear PNe population of M31 is only marginally consistent with the generally adopted form of the PNe luminosity function (PNLF). In particular, this is due to a lack of PNe with absolute magnitude M5007 brighter than -3, which would only result from a rather unfortunate draw from such a model PNLF. We suggest that the observed lack of bright PNe in the nuclear regions of M31 is due to a horizontal-branch population that is more tilted toward less massive and hotter He-burning stars, so that its progeny consists mostly of UV-bright stars that fail to climb back up the asymptotic giant branch (AGB) and only of few, if any, bright PNe powered by central post-AGB stars. These results are also consistent with recent reports on a dearth of bright post-AGB stars towards the nucleus of M31, and lend further support to the idea that the metallicity of a stellar population has an impact on the way the horizontal branch is populated and to the loose anticorrelation between the strength of the UV-upturn and the specific number of PNe that is observed in early-type galaxies. Finally, our investigation also serves to stress the importance of considering the same spatial scales when comparing the PNe population of galaxies with the properties of their stellar populations.
The aim of this work is to identify HeII emitters at 2<z<4.6 and to constrain the source of the hard ionizing continuum that powers the HeII emission. We have assembled a sample of 352 galaxies with a high quality spectroscopic redshift at 2<z<4.6 from the VVDS survey, and we have identified 40 HeII1640A emitters. We study their spectral properties, measuring the fluxes, equivalent widths (EW) and FWHM for most relevant lines. About 10% of galaxies at z~3 show HeII in emission, with rest frame equivalent widths EW0~1-7A, equally distributed between galaxies with Lya in emission or in absorption. We find 12 high-quality HeII emitters with unresolved HeII line (FWHM_0<1200km/s), 13 high-quality emitters with broad He II emission (FWHM_0>1200km/s), 3 AGN, and an additional 12 possible HeII emitters. The properties of the individual broad emitters are in agreement with expectations from a W-R model. On the contrary, the properties of the narrow emitters are not compatible with such model, neither with predictions of gravitational cooling radiation produced by gas accretion. Rather, we find that the EW of the narrow HeII line emitters are in agreement with expectations for a PopIII star formation, if the episode of star formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1 only is enough to sustain the observed HeII flux. We conclude that narrow HeII emitters are either powered by the ionizing flux from a stellar population rare at z~0 but much more common at z~3, or by PopIII star formation. As proposed by Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value predicted by Tornatore et al. (2007).
The mathematical concept of the Newtonian limit of Einstein's field equations in the expanding Friedmann universe is formulated. The geodesic equations of motion of planets and light are derived and compared.
This paper investigates spheroidal galaxies comprising a self-interacting dark matter halo (SIDM) plus de Vaucouleurs stellar distribution. These are coupled only via their shared gravitational field, which is computed consistently from the density profiles. Assuming conservation of mass, momentum and angular momentum, perturbation analyses reveal the galaxy's response to radial disturbance. The modes depend on fundamental dark matter properties, the stellar mass, and the halo's mass and radius. The coupling of stars and dark matter stabilises some haloes that would be unstable as one-fluid models. However the centrally densest haloes are unstable, causing radial flows of SIDM and stars (sometimes in opposite directions). Depending on the dark microphysics, some highly diffuse haloes are also unstable. Unstable galaxies might shed their outskirts or collapse. Observed elliptical galaxies appear to exist in the safe domain. Halo pulsations are possible. The innermost node of SIDM waves may occur within ten half-light radii. Induced stellar ripples may also occur at detectable radii if higher overtones are excited. If any SIDM exists, observational skotoseismology of galaxies could probe DM physics, measure the sizes of specific systems, and perhaps help explain peculiar objects (e.g. some shell galaxies, and the growth of red nuggets).
The unified model of active galactic nuclei (AGN) claims that the properties of AGN depend on the viewing angle of the observer with respect to a toroidal distribution of dust surrounding the nucleus. Both the mid-infrared (MIR) attenuation and continuum luminosity are expected to be related to dust associated with the torus. Therefore, isolating the nuclear component is essential to study the MIR emission of AGN. We have compiled all the T-ReCS spectra (Gemini observatory) available in the N-band for 22 AGN: 5 Type-1 and 17 Type-2 AGN. The high angular resolution of the T-ReCs spectra allows us to probe physical regions of 57 pc (median). We have used a novel pipeline called RedCan capable of producing flux- and wavelength-calibrated spectra for the CanariCam (GTC) and T-ReCS (Gemini) instruments. We have measured the fine-structure [SIV] at 10.5 microns and the PAH at 11.3 microns line strengths together with the silicate absorption/emission features. We have also compiled Spitzer/IRS spectra to understand how spatial resolution influences the results. The 11.3 microns PAH feature is only clearly detected in the nuclear spectra of two AGN, while it is more common in the Spitzer data. For those two objects the AGN emission in NGC7130 accounts for more than 80% of the MIR continuum at 12 microns while in the case of NGC1808 the AGN is not dominating the MIR emission. This is confirmed by the correlation between the MIR and X-ray continuum luminosities. The [SIV] emission line at 10.5 microns, which is believed to originate in the narrow line region, is detected in most AGN. We have found an enhancement of the optical depth at 9.7 microns in the high-angular resolution data for higher values of NH. Clumpy torus models reproduce the observed values only if the host-galaxy properties are taken into account.
We show that Montecarlo simulations of the TP-AGB stellar population in the LMC and SMC galaxies using the CB* models produce LF and color distributions that are in closer agreement with observations than those obtained with the BC03 and CB07 models. This is a progress report of work that will be published elsewhere.
Based on a recently started programme, we report the first search for intranight optical variability among radio-quiet weak-line-quasars (RQWLQs). Eight members of this class were observed on 13 nights in the R-band, such that each source was monitored continuously at least once for a minimum duration of about 3.5 hours, using the recently installed 130 cm telescope at Devasthal, India. Statistical analysis of the differential light curves was carried out using two versions of the F-test. Based on the INOV data acquired so far, the radio-quiet WLQ population appears to exhibit stronger INOV activity as compared to the general population of radio-quiet quasars (RQQs), but similar to the INOV known for radio-loud quasars of non-blazar type. To improve upon this early result, as well as extend the comparison to blazars, a factor of ?2 improvement in the INOV detection threshold would be needed. Such efforts are underway, motivated by the objective to search for the elusive radio-quiet blazars using INOV observations.
Heuristic approaches in cosmology bypass more difficult calculations that would more strictly agree with the standard Einstein equation. These give us the well-known Friedmann-Lemaitre-Robertson-Walker (FLRW) models, and, more recently, the feedback effect of the global topology of spatial sections on the acceleration of test particles. Forcing the FLRW heuristic model on observations leads to dark energy, which, pending fully relativistic calculations, is best interpreted as an artefact. Could topological acceleration also be an artefact of using a heuristic approach? A multiply connected exact solution of the Einstein equation shows that topological acceleration is present in at least one fully relativistic case---it is not an artefact of Newtonian-like thinking.
According to the Big Bang theory and as a consequence of adiabatic expansion of the Universe, the temperature of the cosmic microwave background (CMB) increases linearly with redshift. This relation is, however, poorly explored, and detection of any deviation would directly lead to (astro-)physics beyond the standard model. We aim at measuring the temperature of the CMB with an accuracy of a few percent at z=0.89 toward the molecular absorber in the galaxy lensing the quasar PKS1830-211. We adopt a Monte-Carlo Markov Chain approach, coupled with predictions from the non-LTE radiative transfer code RADEX, to solve the excitation of a set of various molecular species directly from their spectra. We determine Tcmb=5.08 pm 0.10 K at 68% confidence level. Our measurement is consistent with the value Tcmb=5.14 K predicted by the standard cosmological model with adiabatic expansion of the Universe. This is the most precise determination of Tcmb at z>0 to date.
We demonstrate that any scaling source in the radiation era produces a background of gravitational waves with an exact scale-invariant power spectrum. Cosmic defects, created after a phase transition in the early Universe, are such a scaling source. We emphasise that the result is independent of the topology of the cosmic defects, the order of phase transition, and the nature of the symmetry broken, global or gauged. As an example, using large-scale numerical simulations, we calculate the scale invariant gravitational wave power spectrum generated by the dynamics of a global O(N) scalar theory. The result approaches the large N theoretical prediction as N^(-2), albeit with a large coefficient. The signal from global cosmic strings is O(100) times larger than the large N prediction.
The shape of the OB-star spectral energy distribution is a critical component in many diagnostics of the ISM and galaxy properties. We use single-star HII regions from the LMC to quantitatively examine the ionizing SEDs from widely available CoStar, TLUSTY, and WM-basic atmosphere grids. We evaluate the stellar atmosphere models by matching the emission-line spectra that they predict from CLOUDY photoionization simulations with those observed from the nebulae. The atmosphere models are able to reproduce the observed optical nebular line ratios, except at the highest energy transitions > 40 eV, assuming that the gas distribution is non-uniform. Overall we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rate of ionizing photons produced by the model SEDs is consistent with the rate derived from the \Halpha\ luminosity for standard, log(g) = 4.0 models adopted from the atmosphere grids. However, there is a systematic offset between the rate of ionizing photons from different atmosphere models that is correlated with the relative hardness of the SEDs. In general WM-basic and TLUSTY atmosphere models predict similar effective temperatures, while CoStar predicts effective temperatures that are cooler by a few thousand degrees. We compare our effective temperatures, which depend on the nebular ionization balance, to conventional photospheric-based calibrations from the literature. We suggest that in the future, spectral type to effective temperature calibrations can be constructed from nebular data.
A brief history of the discovery of the expanding universe is presented, with an emphasis on the seminal contribution of VM Slipher. It is suggested that the well-known Hubble graph of 1929 could also be known as the Hubble-Slipher graph. It is also argued that the discovery of the expanding universe matches the traditional view of scientific advance as a gradual process of discovery and acceptance, and does not concur with the Kuhnian view of science progressing via abrupt paradigm shifts.
Links to: arXiv, form interface, find, astro-ph, recent, 1212, contact, help (Access key information)
We study the cosmological evolution for a universe in the presence of a continuous tower of massive scalar fields which can drive the current phase of accelerated expansion of the universe and, in addition, can contribute as a dark matter component. The tower consists of a continuous set of massive scalar fields with a gaussian mass distribution. We show that, in a certain region of the parameter space, the {\it heavy} modes of the tower (those with masses much larger than the Hubble expansion rate) dominate at early times and make the tower behave like the usual single scalar field whose coherent oscillations around the minimum of the potential give a matter-like contribution. On the other hand, at late times, the {\it light} modes (those with masses much smaller than the Hubble expansion rate) overcome the energy density of the tower and they behave like a perfect fluid with equation of state ranging from 0 to -1, depending on the spectral index of the initial spectrum. This is a distinctive feature of the tower with respect to the case of quintessence fields, since a massive scalar field can only give acceleration with equation of state close to -1. Such unique property is the result of a synergy effect between the different mass modes. Interestingly, we find that, for some choices of the spectral index, the tower tracks the matter component at high redshifts (or it can even play the role of the dark matter) and eventually become the dominant component of the universe and give rise to an accelerated expansion.
Following a first study of the central regions of M32 that illustrated the power of integral-field spectroscopy (IFS) in detecting and measuring the [O III]{\lambda}5007 emission of PNe against a strong stellar background, we turn to the very nuclear PN population of M31, within 80 pc of its centre. We show that PNe can also be found in the presence of emission from diffuse gas and further illustrate the excellent sensitivity of IFS in detecting extragalactic PNe through a comparison with narrowband images obtained with the Hubble Space Telescope. We find the nuclear PNe population of M31 is only marginally consistent with the generally adopted form of the PNe luminosity function (PNLF). In particular, this is due to a lack of PNe with absolute magnitude M5007 brighter than -3, which would only result from a rather unfortunate draw from such a model PNLF. We suggest that the observed lack of bright PNe in the nuclear regions of M31 is due to a horizontal-branch population that is more tilted toward less massive and hotter He-burning stars, so that its progeny consists mostly of UV-bright stars that fail to climb back up the asymptotic giant branch (AGB) and only of few, if any, bright PNe powered by central post-AGB stars. These results are also consistent with recent reports on a dearth of bright post-AGB stars towards the nucleus of M31, and lend further support to the idea that the metallicity of a stellar population has an impact on the way the horizontal branch is populated and to the loose anticorrelation between the strength of the UV-upturn and the specific number of PNe that is observed in early-type galaxies. Finally, our investigation also serves to stress the importance of considering the same spatial scales when comparing the PNe population of galaxies with the properties of their stellar populations.
The aim of this work is to identify HeII emitters at 2<z<4.6 and to constrain the source of the hard ionizing continuum that powers the HeII emission. We have assembled a sample of 352 galaxies with a high quality spectroscopic redshift at 2<z<4.6 from the VVDS survey, and we have identified 40 HeII1640A emitters. We study their spectral properties, measuring the fluxes, equivalent widths (EW) and FWHM for most relevant lines. About 10% of galaxies at z~3 show HeII in emission, with rest frame equivalent widths EW0~1-7A, equally distributed between galaxies with Lya in emission or in absorption. We find 12 high-quality HeII emitters with unresolved HeII line (FWHM_0<1200km/s), 13 high-quality emitters with broad He II emission (FWHM_0>1200km/s), 3 AGN, and an additional 12 possible HeII emitters. The properties of the individual broad emitters are in agreement with expectations from a W-R model. On the contrary, the properties of the narrow emitters are not compatible with such model, neither with predictions of gravitational cooling radiation produced by gas accretion. Rather, we find that the EW of the narrow HeII line emitters are in agreement with expectations for a PopIII star formation, if the episode of star formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1 only is enough to sustain the observed HeII flux. We conclude that narrow HeII emitters are either powered by the ionizing flux from a stellar population rare at z~0 but much more common at z~3, or by PopIII star formation. As proposed by Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value predicted by Tornatore et al. (2007).
The mathematical concept of the Newtonian limit of Einstein's field equations in the expanding Friedmann universe is formulated. The geodesic equations of motion of planets and light are derived and compared.
This paper investigates spheroidal galaxies comprising a self-interacting dark matter halo (SIDM) plus de Vaucouleurs stellar distribution. These are coupled only via their shared gravitational field, which is computed consistently from the density profiles. Assuming conservation of mass, momentum and angular momentum, perturbation analyses reveal the galaxy's response to radial disturbance. The modes depend on fundamental dark matter properties, the stellar mass, and the halo's mass and radius. The coupling of stars and dark matter stabilises some haloes that would be unstable as one-fluid models. However the centrally densest haloes are unstable, causing radial flows of SIDM and stars (sometimes in opposite directions). Depending on the dark microphysics, some highly diffuse haloes are also unstable. Unstable galaxies might shed their outskirts or collapse. Observed elliptical galaxies appear to exist in the safe domain. Halo pulsations are possible. The innermost node of SIDM waves may occur within ten half-light radii. Induced stellar ripples may also occur at detectable radii if higher overtones are excited. If any SIDM exists, observational skotoseismology of galaxies could probe DM physics, measure the sizes of specific systems, and perhaps help explain peculiar objects (e.g. some shell galaxies, and the growth of red nuggets).
The unified model of active galactic nuclei (AGN) claims that the properties of AGN depend on the viewing angle of the observer with respect to a toroidal distribution of dust surrounding the nucleus. Both the mid-infrared (MIR) attenuation and continuum luminosity are expected to be related to dust associated with the torus. Therefore, isolating the nuclear component is essential to study the MIR emission of AGN. We have compiled all the T-ReCS spectra (Gemini observatory) available in the N-band for 22 AGN: 5 Type-1 and 17 Type-2 AGN. The high angular resolution of the T-ReCs spectra allows us to probe physical regions of 57 pc (median). We have used a novel pipeline called RedCan capable of producing flux- and wavelength-calibrated spectra for the CanariCam (GTC) and T-ReCS (Gemini) instruments. We have measured the fine-structure [SIV] at 10.5 microns and the PAH at 11.3 microns line strengths together with the silicate absorption/emission features. We have also compiled Spitzer/IRS spectra to understand how spatial resolution influences the results. The 11.3 microns PAH feature is only clearly detected in the nuclear spectra of two AGN, while it is more common in the Spitzer data. For those two objects the AGN emission in NGC7130 accounts for more than 80% of the MIR continuum at 12 microns while in the case of NGC1808 the AGN is not dominating the MIR emission. This is confirmed by the correlation between the MIR and X-ray continuum luminosities. The [SIV] emission line at 10.5 microns, which is believed to originate in the narrow line region, is detected in most AGN. We have found an enhancement of the optical depth at 9.7 microns in the high-angular resolution data for higher values of NH. Clumpy torus models reproduce the observed values only if the host-galaxy properties are taken into account.
We show that Montecarlo simulations of the TP-AGB stellar population in the LMC and SMC galaxies using the CB* models produce LF and color distributions that are in closer agreement with observations than those obtained with the BC03 and CB07 models. This is a progress report of work that will be published elsewhere.
Based on a recently started programme, we report the first search for intranight optical variability among radio-quiet weak-line-quasars (RQWLQs). Eight members of this class were observed on 13 nights in the R-band, such that each source was monitored continuously at least once for a minimum duration of about 3.5 hours, using the recently installed 130 cm telescope at Devasthal, India. Statistical analysis of the differential light curves was carried out using two versions of the F-test. Based on the INOV data acquired so far, the radio-quiet WLQ population appears to exhibit stronger INOV activity as compared to the general population of radio-quiet quasars (RQQs), but similar to the INOV known for radio-loud quasars of non-blazar type. To improve upon this early result, as well as extend the comparison to blazars, a factor of ?2 improvement in the INOV detection threshold would be needed. Such efforts are underway, motivated by the objective to search for the elusive radio-quiet blazars using INOV observations.
Heuristic approaches in cosmology bypass more difficult calculations that would more strictly agree with the standard Einstein equation. These give us the well-known Friedmann-Lemaitre-Robertson-Walker (FLRW) models, and, more recently, the feedback effect of the global topology of spatial sections on the acceleration of test particles. Forcing the FLRW heuristic model on observations leads to dark energy, which, pending fully relativistic calculations, is best interpreted as an artefact. Could topological acceleration also be an artefact of using a heuristic approach? A multiply connected exact solution of the Einstein equation shows that topological acceleration is present in at least one fully relativistic case---it is not an artefact of Newtonian-like thinking.
According to the Big Bang theory and as a consequence of adiabatic expansion of the Universe, the temperature of the cosmic microwave background (CMB) increases linearly with redshift. This relation is, however, poorly explored, and detection of any deviation would directly lead to (astro-)physics beyond the standard model. We aim at measuring the temperature of the CMB with an accuracy of a few percent at z=0.89 toward the molecular absorber in the galaxy lensing the quasar PKS1830-211. We adopt a Monte-Carlo Markov Chain approach, coupled with predictions from the non-LTE radiative transfer code RADEX, to solve the excitation of a set of various molecular species directly from their spectra. We determine Tcmb=5.08 pm 0.10 K at 68% confidence level. Our measurement is consistent with the value Tcmb=5.14 K predicted by the standard cosmological model with adiabatic expansion of the Universe. This is the most precise determination of Tcmb at z>0 to date.
We demonstrate that any scaling source in the radiation era produces a background of gravitational waves with an exact scale-invariant power spectrum. Cosmic defects, created after a phase transition in the early Universe, are such a scaling source. We emphasise that the result is independent of the topology of the cosmic defects, the order of phase transition, and the nature of the symmetry broken, global or gauged. As an example, using large-scale numerical simulations, we calculate the scale invariant gravitational wave power spectrum generated by the dynamics of a global O(N) scalar theory. The result approaches the large N theoretical prediction as N^(-2), albeit with a large coefficient. The signal from global cosmic strings is O(100) times larger than the large N prediction.
The shape of the OB-star spectral energy distribution is a critical component in many diagnostics of the ISM and galaxy properties. We use single-star HII regions from the LMC to quantitatively examine the ionizing SEDs from widely available CoStar, TLUSTY, and WM-basic atmosphere grids. We evaluate the stellar atmosphere models by matching the emission-line spectra that they predict from CLOUDY photoionization simulations with those observed from the nebulae. The atmosphere models are able to reproduce the observed optical nebular line ratios, except at the highest energy transitions > 40 eV, assuming that the gas distribution is non-uniform. Overall we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rate of ionizing photons produced by the model SEDs is consistent with the rate derived from the \Halpha\ luminosity for standard, log(g) = 4.0 models adopted from the atmosphere grids. However, there is a systematic offset between the rate of ionizing photons from different atmosphere models that is correlated with the relative hardness of the SEDs. In general WM-basic and TLUSTY atmosphere models predict similar effective temperatures, while CoStar predicts effective temperatures that are cooler by a few thousand degrees. We compare our effective temperatures, which depend on the nebular ionization balance, to conventional photospheric-based calibrations from the literature. We suggest that in the future, spectral type to effective temperature calibrations can be constructed from nebular data.
A brief history of the discovery of the expanding universe is presented, with an emphasis on the seminal contribution of VM Slipher. It is suggested that the well-known Hubble graph of 1929 could also be known as the Hubble-Slipher graph. It is also argued that the discovery of the expanding universe matches the traditional view of scientific advance as a gradual process of discovery and acceptance, and does not concur with the Kuhnian view of science progressing via abrupt paradigm shifts.
Links to: arXiv, form interface, find, astro-ph, recent, 1212, contact, help (Access key information)
We study the cosmological evolution for a universe in the presence of a continuous tower of massive scalar fields which can drive the current phase of accelerated expansion of the universe and, in addition, can contribute as a dark matter component. The tower consists of a continuous set of massive scalar fields with a gaussian mass distribution. We show that, in a certain region of the parameter space, the {\it heavy} modes of the tower (those with masses much larger than the Hubble expansion rate) dominate at early times and make the tower behave like the usual single scalar field whose coherent oscillations around the minimum of the potential give a matter-like contribution. On the other hand, at late times, the {\it light} modes (those with masses much smaller than the Hubble expansion rate) overcome the energy density of the tower and they behave like a perfect fluid with equation of state ranging from 0 to -1, depending on the spectral index of the initial spectrum. This is a distinctive feature of the tower with respect to the case of quintessence fields, since a massive scalar field can only give acceleration with equation of state close to -1. Such unique property is the result of a synergy effect between the different mass modes. Interestingly, we find that, for some choices of the spectral index, the tower tracks the matter component at high redshifts (or it can even play the role of the dark matter) and eventually become the dominant component of the universe and give rise to an accelerated expansion.
Following a first study of the central regions of M32 that illustrated the power of integral-field spectroscopy (IFS) in detecting and measuring the [O III]{\lambda}5007 emission of PNe against a strong stellar background, we turn to the very nuclear PN population of M31, within 80 pc of its centre. We show that PNe can also be found in the presence of emission from diffuse gas and further illustrate the excellent sensitivity of IFS in detecting extragalactic PNe through a comparison with narrowband images obtained with the Hubble Space Telescope. We find the nuclear PNe population of M31 is only marginally consistent with the generally adopted form of the PNe luminosity function (PNLF). In particular, this is due to a lack of PNe with absolute magnitude M5007 brighter than -3, which would only result from a rather unfortunate draw from such a model PNLF. We suggest that the observed lack of bright PNe in the nuclear regions of M31 is due to a horizontal-branch population that is more tilted toward less massive and hotter He-burning stars, so that its progeny consists mostly of UV-bright stars that fail to climb back up the asymptotic giant branch (AGB) and only of few, if any, bright PNe powered by central post-AGB stars. These results are also consistent with recent reports on a dearth of bright post-AGB stars towards the nucleus of M31, and lend further support to the idea that the metallicity of a stellar population has an impact on the way the horizontal branch is populated and to the loose anticorrelation between the strength of the UV-upturn and the specific number of PNe that is observed in early-type galaxies. Finally, our investigation also serves to stress the importance of considering the same spatial scales when comparing the PNe population of galaxies with the properties of their stellar populations.
The aim of this work is to identify HeII emitters at 2<z<4.6 and to constrain the source of the hard ionizing continuum that powers the HeII emission. We have assembled a sample of 352 galaxies with a high quality spectroscopic redshift at 2<z<4.6 from the VVDS survey, and we have identified 40 HeII1640A emitters. We study their spectral properties, measuring the fluxes, equivalent widths (EW) and FWHM for most relevant lines. About 10% of galaxies at z~3 show HeII in emission, with rest frame equivalent widths EW0~1-7A, equally distributed between galaxies with Lya in emission or in absorption. We find 12 high-quality HeII emitters with unresolved HeII line (FWHM_0<1200km/s), 13 high-quality emitters with broad He II emission (FWHM_0>1200km/s), 3 AGN, and an additional 12 possible HeII emitters. The properties of the individual broad emitters are in agreement with expectations from a W-R model. On the contrary, the properties of the narrow emitters are not compatible with such model, neither with predictions of gravitational cooling radiation produced by gas accretion. Rather, we find that the EW of the narrow HeII line emitters are in agreement with expectations for a PopIII star formation, if the episode of star formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1 only is enough to sustain the observed HeII flux. We conclude that narrow HeII emitters are either powered by the ionizing flux from a stellar population rare at z~0 but much more common at z~3, or by PopIII star formation. As proposed by Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value predicted by Tornatore et al. (2007).
The mathematical concept of the Newtonian limit of Einstein's field equations in the expanding Friedmann universe is formulated. The geodesic equations of motion of planets and light are derived and compared.
This paper investigates spheroidal galaxies comprising a self-interacting dark matter halo (SIDM) plus de Vaucouleurs stellar distribution. These are coupled only via their shared gravitational field, which is computed consistently from the density profiles. Assuming conservation of mass, momentum and angular momentum, perturbation analyses reveal the galaxy's response to radial disturbance. The modes depend on fundamental dark matter properties, the stellar mass, and the halo's mass and radius. The coupling of stars and dark matter stabilises some haloes that would be unstable as one-fluid models. However the centrally densest haloes are unstable, causing radial flows of SIDM and stars (sometimes in opposite directions). Depending on the dark microphysics, some highly diffuse haloes are also unstable. Unstable galaxies might shed their outskirts or collapse. Observed elliptical galaxies appear to exist in the safe domain. Halo pulsations are possible. The innermost node of SIDM waves may occur within ten half-light radii. Induced stellar ripples may also occur at detectable radii if higher overtones are excited. If any SIDM exists, observational skotoseismology of galaxies could probe DM physics, measure the sizes of specific systems, and perhaps help explain peculiar objects (e.g. some shell galaxies, and the growth of red nuggets).
The unified model of active galactic nuclei (AGN) claims that the properties of AGN depend on the viewing angle of the observer with respect to a toroidal distribution of dust surrounding the nucleus. Both the mid-infrared (MIR) attenuation and continuum luminosity are expected to be related to dust associated with the torus. Therefore, isolating the nuclear component is essential to study the MIR emission of AGN. We have compiled all the T-ReCS spectra (Gemini observatory) available in the N-band for 22 AGN: 5 Type-1 and 17 Type-2 AGN. The high angular resolution of the T-ReCs spectra allows us to probe physical regions of 57 pc (median). We have used a novel pipeline called RedCan capable of producing flux- and wavelength-calibrated spectra for the CanariCam (GTC) and T-ReCS (Gemini) instruments. We have measured the fine-structure [SIV] at 10.5 microns and the PAH at 11.3 microns line strengths together with the silicate absorption/emission features. We have also compiled Spitzer/IRS spectra to understand how spatial resolution influences the results. The 11.3 microns PAH feature is only clearly detected in the nuclear spectra of two AGN, while it is more common in the Spitzer data. For those two objects the AGN emission in NGC7130 accounts for more than 80% of the MIR continuum at 12 microns while in the case of NGC1808 the AGN is not dominating the MIR emission. This is confirmed by the correlation between the MIR and X-ray continuum luminosities. The [SIV] emission line at 10.5 microns, which is believed to originate in the narrow line region, is detected in most AGN. We have found an enhancement of the optical depth at 9.7 microns in the high-angular resolution data for higher values of NH. Clumpy torus models reproduce the observed values only if the host-galaxy properties are taken into account.
We show that Montecarlo simulations of the TP-AGB stellar population in the LMC and SMC galaxies using the CB* models produce LF and color distributions that are in closer agreement with observations than those obtained with the BC03 and CB07 models. This is a progress report of work that will be published elsewhere.
Based on a recently started programme, we report the first search for intranight optical variability among radio-quiet weak-line-quasars (RQWLQs). Eight members of this class were observed on 13 nights in the R-band, such that each source was monitored continuously at least once for a minimum duration of about 3.5 hours, using the recently installed 130 cm telescope at Devasthal, India. Statistical analysis of the differential light curves was carried out using two versions of the F-test. Based on the INOV data acquired so far, the radio-quiet WLQ population appears to exhibit stronger INOV activity as compared to the general population of radio-quiet quasars (RQQs), but similar to the INOV known for radio-loud quasars of non-blazar type. To improve upon this early result, as well as extend the comparison to blazars, a factor of ?2 improvement in the INOV detection threshold would be needed. Such efforts are underway, motivated by the objective to search for the elusive radio-quiet blazars using INOV observations.
Heuristic approaches in cosmology bypass more difficult calculations that would more strictly agree with the standard Einstein equation. These give us the well-known Friedmann-Lemaitre-Robertson-Walker (FLRW) models, and, more recently, the feedback effect of the global topology of spatial sections on the acceleration of test particles. Forcing the FLRW heuristic model on observations leads to dark energy, which, pending fully relativistic calculations, is best interpreted as an artefact. Could topological acceleration also be an artefact of using a heuristic approach? A multiply connected exact solution of the Einstein equation shows that topological acceleration is present in at least one fully relativistic case---it is not an artefact of Newtonian-like thinking.
According to the Big Bang theory and as a consequence of adiabatic expansion of the Universe, the temperature of the cosmic microwave background (CMB) increases linearly with redshift. This relation is, however, poorly explored, and detection of any deviation would directly lead to (astro-)physics beyond the standard model. We aim at measuring the temperature of the CMB with an accuracy of a few percent at z=0.89 toward the molecular absorber in the galaxy lensing the quasar PKS1830-211. We adopt a Monte-Carlo Markov Chain approach, coupled with predictions from the non-LTE radiative transfer code RADEX, to solve the excitation of a set of various molecular species directly from their spectra. We determine Tcmb=5.08 pm 0.10 K at 68% confidence level. Our measurement is consistent with the value Tcmb=5.14 K predicted by the standard cosmological model with adiabatic expansion of the Universe. This is the most precise determination of Tcmb at z>0 to date.
We demonstrate that any scaling source in the radiation era produces a background of gravitational waves with an exact scale-invariant power spectrum. Cosmic defects, created after a phase transition in the early Universe, are such a scaling source. We emphasise that the result is independent of the topology of the cosmic defects, the order of phase transition, and the nature of the symmetry broken, global or gauged. As an example, using large-scale numerical simulations, we calculate the scale invariant gravitational wave power spectrum generated by the dynamics of a global O(N) scalar theory. The result approaches the large N theoretical prediction as N^(-2), albeit with a large coefficient. The signal from global cosmic strings is O(100) times larger than the large N prediction.
The shape of the OB-star spectral energy distribution is a critical component in many diagnostics of the ISM and galaxy properties. We use single-star HII regions from the LMC to quantitatively examine the ionizing SEDs from widely available CoStar, TLUSTY, and WM-basic atmosphere grids. We evaluate the stellar atmosphere models by matching the emission-line spectra that they predict from CLOUDY photoionization simulations with those observed from the nebulae. The atmosphere models are able to reproduce the observed optical nebular line ratios, except at the highest energy transitions > 40 eV, assuming that the gas distribution is non-uniform. Overall we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rate of ionizing photons produced by the model SEDs is consistent with the rate derived from the \Halpha\ luminosity for standard, log(g) = 4.0 models adopted from the atmosphere grids. However, there is a systematic offset between the rate of ionizing photons from different atmosphere models that is correlated with the relative hardness of the SEDs. In general WM-basic and TLUSTY atmosphere models predict similar effective temperatures, while CoStar predicts effective temperatures that are cooler by a few thousand degrees. We compare our effective temperatures, which depend on the nebular ionization balance, to conventional photospheric-based calibrations from the literature. We suggest that in the future, spectral type to effective temperature calibrations can be constructed from nebular data.
A brief history of the discovery of the expanding universe is presented, with an emphasis on the seminal contribution of VM Slipher. It is suggested that the well-known Hubble graph of 1929 could also be known as the Hubble-Slipher graph. It is also argued that the discovery of the expanding universe matches the traditional view of scientific advance as a gradual process of discovery and acceptance, and does not concur with the Kuhnian view of science progressing via abrupt paradigm shifts.
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We report on a measurement of the temperature of the cosmic microwave background radiation field, T_CMB, at z = 0.88582 by imaging HC3N (3-2) and (5-4) absorption in the foreground galaxy of the gravitationally lens magnified radio source PKS 1830-211 using the Very Long Baseline Array and the phased Very Large Array. Low-resolution imaging of the data yields a value of Trot = 5.6+2.5-0.9 K, for the rotational temperature, Trot, which is consistent with the temperature of the cosmic microwave background at the absorber's redshift of 2.73(1+z) K. However, our high-resolution imaging reveals that the absorption peak position of the foreground gas is offset from the continuum peak position of the synchrotron radiation from PKS 1830-211 SW, which indicates that the absorbing cloud is covering only part of the emission from PKS 1830-211, rather than the entire core-jet region. This changes the line-to-continuum ratios, and we find Trot between 1.1 and 2.5 K, which is lower than the expected value. This shows that previous, Trot, measurements could be biased due to unresolved structure.
Due to its proximity, the mass of the supermassive black hole in the nucleus of Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk that surrounds it. We report here the discovery of an eccentric Halpha emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0_{-1.0}^{+0.8} x 10^7 Mo for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1-sigma level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-sigma relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the Halpha emitting disk. This result suggests that the stellar and the Halpha emitting disks are intrinsically different from each other. A plausible explanation is that the Halpha emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the Halpha emission is, at least partially, generated by stars.
This paper presents a review of the topic of galaxy formation and evolution, focusing on basic features of galaxies, and how these observables reveal how galaxies and their stars assemble over cosmic time. I give an overview of the observed properties of galaxies in the nearby universe and for those at higher redshifts up to z~10. This includes a discussion of the major processes in which galaxies assemble and how we can now observe these - including the merger history of galaxies, the gas accretion and star formation rates. I show that for the most massive galaxies mergers and accretion are about equally important in the galaxy formation process between z = 1-3, while this likely differs for lower mass systems. I also discuss the mass differential evolution for galaxies, as well as how environment can affect galaxy evolution, although mass is the primary criteria for driving evolution. I also discuss how we are beginning to measure the dark matter content of galaxies at different epochs as measured through kinematics and clustering. Finally, I review how observables of galaxies, and the observed galaxy formation process, compares with predictions from simulations of galaxy formation, finding significant discrepancies in the abundances of massive galaxies and the merger history. I conclude by examining prospects for the future using JWST, Euclid, SKA, and the ELTs in addressing outstanding issues.
The Circumgalactic Medium (CGM) of late-type galaxies is characterized using UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph. CGM warm cloud properties are derived, including volume filling factors of 3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5 virial radii are metal-bearing and many have velocities consistent with being bound, "galactic fountain" clouds. For galaxies with L > 0.1 L*, the total mass in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total baryons in massive spirals and comparable to the baryons in their parent galaxy disks. This leaves >50% of massive spiral-galaxy baryons "missing". Dwarfs (<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon fraction), suggesting that many of their warm clouds escape. Constant warm cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3} K) support the inference that previous COS detections of broad, shallow O VI and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K) intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM clouds cannot account for all the "missing baryons" in spirals, the hot intra-group gas can, and could account for ~20% of the cosmic baryon census at z ~ 0 if this hot gas is ubiquitous among spiral groups.
If the Galactic WMAP radio haze, as recently confirmed by Planck, is produced by dark matter annihilation or decay, similar diffuse radio halos should exist around other galaxies with physical properties comparable to the Milky Way. If instead the haze is due to an astrophysical mechanism peculiar to the Milky Way or to a transient event, a similar halo need not exist around all Milky Way "twins". We use radio observations of 66 spiral galaxies to test the dark matter origin of the haze. We select galaxies based on morphological type and maximal rotational velocity, and obtain their luminosities from a 1.49 GHz catalog and additional radio observations at other frequencies. We find many instances of galaxies with radio emission that is less than 5% as bright as naively expected from dark matter models that could produce the Milky Way haze, and at least 3 galaxies that are less than 1% as bright as expected, assuming dark matter distributions, magnetic fields, and cosmic ray propagation parameters equal to those of the Milky Way. For reasonable ranges for the variation of these parameters, we estimate the fraction of galaxies that should be expected to be significantly less bright in radio, and argue that this is marginally compatible with the observed distribution. While our findings therefore cannot rule out a dark matter origin for the radio haze at this time, we find numerous examples (including the Andromeda Galaxy) where, if dark matter is indeed the origin of the Milky Way haze, some mechanism must be in place to suppress the corresponding haze of the external galaxy. We point out that Planck data will offer opportunities to improve this type of constraint in a highly relevant frequency range and for a potentially larger set of candidate galaxies.
In this Letter, we propose a new generalized Ricci dark energy (NGR) model to
unify Ricci dark energy (RDE) and XCDM. Our model can distinguish between RDE
and XCDM by introducing a parameter $\beta$ called weight factor. When
$\beta=1$, NGR model becomes the usual RDE model. The XCDM model is
corresponding to $\beta=0$. Moreover, NGR model permits the situation where
neither $\beta=1$ nor $\beta=0$. We then perform a statefinder analysis on NGR
model to see how $\beta$ effects the trajectory on the $r-s$ plane.
In order to know the value of $\beta$, we constrain NGR model with latest
observations including type Ia supernovae (SNe Ia) from Union2 set (557 data),
baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan
Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and cosmic
microwave background (CMB) observation from the 7-year Wilkinson Microwave
Anisotropy Probe (WMAP7) results. With Markov Chain Monte Carlo (MCMC) method,
the constraint result is
$\beta$=$0.08_{-0.21}^{+0.30}(1\sigma)_{-0.28}^{+0.43}(2\sigma)$, which
manifests the observations prefer a XCDM universe rather than RDE model. It
seems RDE model is ruled out in NGR scenario within $2\sigma$ regions.
Furthermore, we compare it with some of successful cosmological models using
AIC information criterion. NGR model seems to be a good choice for describing
the universe.
We analyze the possibility to distinguish between quintessence and phantom scalar field models of dark energy using observations of luminosity distance moduli of SNe Ia, CMB anisotropies and polarization, matter density perturbations and baryon acoustic oscillations. None of the present observations can decide between quintessence or phantom scalar field models at a statistically significant level: for each model a set of best-fit parameters exists, which matches all data with similar goodness of fit. We compare the relative differences of best-fit model predictions with observational uncertainties for each type of data and we show that the accuracy of SNe Ia luminosity distance data is far from the one necessary to distinguish these types of dark energy models, while the CMB data (WMAP, SPT and Planck) are close to being able to distinguish them. Also a significant improvement of the large-scale structure data (e.g. Euclid or BigBOSS) will enable us to decide between quintessence and phantom dark energy.
We propose a method of calculation of the power spectrum of cosmological perturbations by means of a direct numerical integration of hydrodynamic equations in the Fourier space for a random ensemble of initial conditions with subsequent averaging procedure. This method can be an alternative to the cosmological N-body simulations. We test realizability of this method in case of one-dimensional motion of gravitating matter pressureless shells. In order to test the numerical simulations, we found an analytical solution which describes one-dimensional collapse of plane shells. The results are used to study a nonlinear interaction of different Fourier modes.
Sources generating most of the X-ray background (XRB) are dispersed over a wide range of redshifts. Thus, statistical characteristics of the source distribution carry the information on the matter distribution on very large scales. We test the possibility to detect the variation of the X-ray source number counts over the celestial sphere. A large number of Chandra pointings spread over both galactic hemispheres is investigated. A search for all the point-like sources in the soft band of 0.5 - 2 keV is performed, and statistical assessment of the population of sources below the detection threshold is carried out. A homogeneous sample of the number counts at fluxes above ~10^{-16} erg/s/cm^2 for more than 300 ACIS fields was constructed. The counts correlations between overlapping fields were used to assess the accuracy of the computational methods used in the analysis. It is shown that the source number counts vary between fields at the level only slightly larger than the fluctuation amplitude expected for the random (Poissonian) distribution. Nevertheless, small asymmetry between galactic hemispheres is present. The average number of sources in the northern hemisphere is larger than in the southern at the 2.75 sigma level. Also the autocorrelation function of the source density in both hemispheres are substantially different. Possible explanations for the observed anisotropies are considered. If the effect is unrelated to the observational selection, a large scale inhomogeneities in the distribution of X-ray sources are required. Correlations of the source number counts observed in the southern hemisphere could be generated by a coherent structure extending over 1200 Mpc.
The observational evidence for the acceleration of the universe demonstrates that canonical theories of gravitation and particle physics are incomplete, if not incorrect. A new generation of astronomical facilities will shortly be able to carry out precision consistency tests of the standard cosmological model and search for evidence of new physics beyond it. I describe some of these tests, focusing on the universality of nature's fundamental couplings and the characterization of the properties of dark energy. I will also comment on prospects for forthcoming ESA and ESO facilities in which the CAUP Dark Side team is involved.
The present-day Universe is highly magnetized, even though the first magnetic seed fields were most probably extremely weak. To explain the growth of the magnetic field strength over many orders of magnitude fast amplification processes need to operate. The most efficient mechanism known today is the small-scale dynamo, which converts turbulent kinetic energy into magnetic energy leading to an exponential growth of the magnetic field. The efficiency of the dynamo depends on the type of turbulence indicated by the slope of the turbulence spectrum v(l) \propto l^{theta}, where v(l) is the eddy velocity at a scale l. We explore turbulent spectra ranging from incompressible Kolmogorov turbulence with theta = 1/3 to highly compressible Burgers turbulence with theta = 1/2. In this work we analyze the properties of the small-scale dynamo for low magnetic Prandtl numbers Pm, which denotes the ratio of the magnetic Reynolds number, Rm, to the hydrodynamical one, Re. We solve the Kazantsev equation, which describes the evolution of the small-scale magnetic field, using the WKB approximation. In the limit of low magnetic Prandtl numbers the growth rate is proportional to Rm^{(1-theta)/(1+theta)}. We furthermore discuss the critical magnetic Reynolds number Rm_crit, which is required for small-scale dynamo action. The value of Rm_crit is roughly 100 for Kolmogorov turbulence and 2700 for Burgers. Furthermore, we discuss that Rm_crit provides a stronger constraint in the limit of low Pm than it does for large Pm. We conclude that the small-scale dynamo can operate in the regime of low magnetic Prandtl numbers, if the magnetic Reynolds number is large enough. Thus, the magnetic field amplification on small scales can take place in a broad range of physical environments and amplify week magnetic seed fields on short timescales.
We study CMB constraints on non-Gaussianity from isocurvature perturbations of general types. Specifically, we study CDM/neutrino isocurvature perturbations which are uncorrelated or totally correlated with adiabatic ones. Using the data from the WMAP 7-year observation at V and W bands, we obtained optimal constraints on the nonlinearity parameters of adiabatic and isocurvature perturbations. Our result shows that primordial perturbations are consistent with Gaussian ones at around 2 sigma level for above mentioned isocurvature modes.
An extra dark radiation component can be present in the universe in the form of sterile neutrinos, axions or other very light degrees of freedom which may interact with the dark matter sector. We derive here the cosmological constraints on the dark radiation abundance, on its effective velocity and on its viscosity parameter from current data in dark radiation-dark matter coupled models. The cosmological bounds on the number of extra dark radiation species do not change significantly when considering interacting schemes. We also find that the constraints on the dark radiation effective velocity are degraded by an order of magnitude while the errors on the viscosity parameter are a factor of two larger when considering interacting scenarios. If future Cosmic Microwave Background data are analysed assuming a non interacting model but the dark radiation and the dark matter sectors interact in nature, the reconstructed values for the effective velocity and for the viscosity parameter will be shifted from their standard 1/3 expectation, namely ceff=0.34 (+0.006 -0.003) and cvis=0.29 (+0.002 -0.001) at 95% CL for the future COrE mission data.
This paper is devoted to the study of Noether gauge symmetries of $f(T)$ gravity minimally coupled with a canonical scalar field. We explicitly determine the unknown functions of the theory $f(T),V(\phi), W(\phi)$. We have shown that there are two invariants for this model, one of which defines the Hamiltonian $H$ under time invariance (energy conservation) and the other is related to scaling invariance. We show that the equation of state parameter in the present model can cross the cosmological constant boundary. The behavior of Hubble parameter in our model closely matches to that of $\Lambda$CDM model, thus our model is an alternative to the later.
In a semi-numerical model of reionization, the evolution of ionization fraction is simulated approximately by the ionizing photon to baryon ratio criterion. In this paper we incorporate a semi-analytical model of galaxy formation based on the Millennium II N-body simulation into the semi-numerical modeling of reionization. The semi-analytical model is used to predict the production of ionizing photons, then we use the semi-numerical method to model the reionization process. Such an approach allows more detailed modeling of the reionization, and also connects observations of galaxies at low and high redshifts to the reionization history. The galaxy formation model we use was designed to match the low-$z$ observations, and it also fits the high redshift luminosity function reasonably well, but its prediction on the star formation falls below the observed value, and we find that it also underpredicts the stellar ionizing photon production rate, hence the reionization can not be completed at $z \sim 6$ without taking into account some other potential sources of ionization photons. We also considered simple modifications of the model with more top heavy initial mass functions (IMF), with which the reionization can occur at earlier epochs. The incorporation of the semi-analytical model may also affect the topology of the HI regions during the EoR, and the neutral regions produced by our simulations with the semi-analytical model appeared less poriferous than the simple halo-based models.
XMASS, a low-background, large liquid-xenon detector, was used to search for solar axions that would be produced by bremsstrahlung and Compton effects in the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent limit on the coupling for mass $\ll$ 1keV is $|g_{aee}|< 5.4\times 10^{-11}$ (90% C.L.), which is a factor of two stronger than the existing experimental limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are 1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced the most stringent limit, which is better than that previously derived from astrophysical arguments regarding the Sun to date.
Cluster properties do not seem to be changing significantly during their mature evolution phase, for example they do not seem to show strong dynamical evolution at least up to z~0.5, their galaxy red sequence is already in place at least up to z$\sim$1.2, and their diffuse light content remains stable up to z~0.8. The question is now to know if cluster properties can evolve more significantly at redshifts notably higher than 1. We propose here to see how the properties of the intracluster light (ICL) evolve with redshift by detecting and analysing the ICL in the X-ray cluster CL J1449+0856 at z=2.07 (discovered by Gobat et al. 2011), based on deep HST NICMOS H band exposures.We used the same wavelet-based method as that applied to 10 clusters between z=0.4 and 0.8 by Guennou et al. (2012). We detect three diffuse light sources with respective total magnitudes of H=24.8, 25.5, and 25.9, plus a more compact object with a magnitude H=25.3. We discuss the significance of our detections and show that they are robust. The three sources of diffuse light indicate an elongation along a north-east south-west axis, similar to that of the distribution of the central galaxies and to the X-ray elongation. This strongly suggests a history of merging events along this direction. While Guennou et al. (2012) found a roughly constant amount of diffuse light for clusters between z~0 and 0.8, we put in evidence at least a 1.5 magnitude increase between z~0.8 and 2. If we assume that the amount of diffuse light is directly linked to the infall activity on the cluster, this implies that CL J1449+0856 is still undergoing strong merging events.
We present multiwavelength X-ray, optical and radio study of the Fanaroff & Riley class I radio galaxy CTD 86 based on \xmm{}, \rosat{}, Sloan Digital Sky Survey (SDSS), Vainu Bappu Telescope (VBT) observations and the Faint Images of the Radio Sky at Twenty centimeters (FIRST) survey. X-ray emission from CTD 86 originates from two components - diffuse thermal emission from hot gas ($kT\sim 0.9\kev$, $n_e\sim 10^{-3}{\rm cm^{-3}}$, $L_X \sim 5\times10^{42}{\rm ergs s^{-1}}$ and size $\sim 186{\rm kpc}$), and a central point source representing the active nucleus. The hot gaseous environment of CTD 86 is similar to those found in galaxy groups or bright early-type galaxies. We found no clear signature of radio-lobes interacting with the diffuse hot gas. X-ray emission from the active nucleus is well described by an intrinsically absorbed ($N_H \sim 5.9\times10^{22}{\rm cm^{-2}}$) power law ($\Gamma \sim 1.5$) with a $2-10\kev$ luminosity $L_X \sim 2.1\times10^{42}{\rm ergs s^{-1}}$. CTD 86 has a weak optical emission line spectrum typical of type 2 active galactic nuclei (AGN). The nuclear X-ray, H$\alpha$, and radio luminosities of CTD 86 are lower than those of luminous AGN. We have measured the stellar velocity dispersion, $\sigma=182\pm8\kms$, of CTD 86 and estimated the mass of central black hole, $M_{BH}\sim 9\times 10^7{\rm M\odot}$, accreting at a rate of $\dot{m} = L_{bol}/L_{Edd} \sim 4\times10^{-3}$. For more detail see submitted pdf
We study the cosmological perturbations in teleparallel dark energy models in which there is a dynamical scalar field with a non-minimal coupling to gravity. We find that the propagating degrees of freedom are the same as in quintessence cosmology despite that variables of the perturbed vierbein field are greater than those in metric theories. The resulting growth evolution shows that gravitational interactions are enhanced during the unique tracker evolution of teleparallel dark energy models.
We study the link between the X-ray emission in radio-quiet AGNs and the accretion rate on the central Supermassive Black-Hole (SMBH) using a well-defined and statistically complete sample of 70 type1 AGNs extracted from the XMM-Newton Bright Serendipitous survey (XBS). To this end, we search and quantify the statistical correlations between the main parameters that characterize the X-ray emission (i.e. the X-ray spectral slope and the X-ray loudness), and the accretion rate, both absolute and relative to the Eddington limit (Eddington ratio). Here, we summarize and discuss the main statistical correlations found and their possible implications on current disk-corona models.
In this brief article, I summarize attempts with collaborators over the last couple of years to extend the Galileon idea in two important ways. I discuss the effective field theory construction arising from co-dimension greater than one flat branes embedded in a flat background - the multi-Galileons - and then describe symmetric covariant versions of the Galileons, more suitable for general cosmological applications. These generalized Galileons can be thought of as interesting four-dimensional field theories in their own rights, but the work described here may also make it easier to embed them into higher dimensional theories. I also briefly mention some intriguing properties, including freedom from ghosts and a non-renormalization theorem, that hint at possible applications in particle physics and cosmology
We find that the cold gas can be magnetically launched from the disc surface with the help of the radiation pressure if the angular velocity of the radiation pressure dominated accretion disc is greater than a critical value, which decreases with increasing the disc thickness H/R (radiation pressure). This indicates the force exerted by the radiation from the disc indeed helps launching the outflow. The rotational velocity of the gas in the disc depends on the strength of the magnetic field threading the disc and the inclination B_z/B_r of the field line at the disc surface. The launching condition for the cold gas at the disc surface sets an upper limit on the magnetic field strength, which is a function of the field line inclination B_z/B_r and the disc thickness H/R. This implies a more strict constraint on the maximal jet power can be extracted from a radiation pressure dominated accretion disc than that derived conventionally on the equipartition assumption.
We performed detailed investigation into cosmological perturbation of f(T) theory of gravity coupled with scalar field. Our work emphasizes on the exact way of gauge fixing and we examined all possible modes of perturbations up to second order. This includes in addition to the usual scalar, vector, and tensor modes, also pseudoscalar and pseudovector modes; although we find that there is no gravitational propagating degrees of freedom in the scalar, pseudoscalar, vector, as well as pseudovector modes. We also find that the scalar and tensor perturbations have exactly the same form as their counterparts in usual general relativity with scalar field, except that the factor of reduced Planck mass squared that occurs in the latter has now been replaced by an effective time-dependent gravitational coupling $-2 (df/dT)|_{T=T_0}$, with $T_0$ being the background torsion scalar. The absence of extra degrees of freedom of f(T) gravity at second order linear perturbation indicates that f(T) gravity is highly nonlinear, and one cannot conclusively analyze stability of the theory without performing nonlinear analysis that can reveal the propagation of the extra degrees of freedom.
The extragalactic background light (EBL) contains important information about stellar and galaxy evolution. It leaves imprint on the very high energy $\gamma$-ray spectra from sources at cosmological distances due to the process of pair production. In this work we propose to {\em measure} the EBL directly by extracting the collective attenuation effects in a number of $\gamma$-ray sources at different redshifts. Using a Markov Chain Monte Carlo fitting method, the EBL intensities and the intrinsic spectral parameters of $\gamma$-ray sources are derived simultaneously. No prior shape of EBL is assumed in the fit. With this method, we can for the first time to derive the spectral shape of the EBL model-independently. Our result shows the expected features predicted by the present EBL models and thus support the understanding of the EBL origin.
We have monitored the BL Lac object S5 0716+714 in five intermediate optical wavebands from 2004 September to 2011 April. Here we present the data that include 8661 measurements which represents one of the largest databases obtained for an object at optical domain. A simple analysis of the data indicates that the object was active in most time, and intraday variability was frequently observed. In total, the object varied by 2.614 magnitudes in the $i$ band. Strong bluer-when-brighter chromatism was observed on long, intermediate, and short timescales.
We report on the discovery of a new Milky Way companion stellar system located at (RA, Dec) = (22h10m43s, +14:56:30). The discovery was made using the eighth data release of SDSS after applying an automated method to search for overdensities in the Baryon Oscillation Spectroscopic Survey footprint. Follow-up observations were performed using CFHT-MegaCam, which reveal that this system is comprised of an old stellar population, located at a distance of 31.9+1.0-1.6 kpc, with a half-light radius of r_h = 9.27 +/- 0.88 pc and a concentration parameter of c = 0.82. A systematic isochrone fit to its color-magnitude diagram resulted in log(age) = 10.07+0.05-0.03 and [Fe/H] = -1.58+0.08-0.13 . These quantities are typical of globular clusters in the MW halo. The newly found object is of low stellar mass, whose observed excess relative to the background is caused by 96 +/- 3 stars. The direct integration of its background decontaminated luminosity function leads to an absolute magnitude of MV = -1.21 +/- 0.66. The resulting surface brightness is uV = 27.19 mag/arcsec2 . Its position in the M_V vs. r_h diagram lies close to AM4 and Koposov 1, which are identified as star clusters. The object is most likely a very faint star cluster - one of the faintest and lowest mass systems yet identified.
This talk discusses various aspects of the structure of space-time presenting mechanisms leading to the explanation of the "rigidity" of the manifold and to the emergence of time, i.e. of the Lorentzian signature. The proposed ingredient is the analog, in four dimensions, of the deformation energy associated with the common threedimensional elasticity theory. The inclusion of this additional term in the Lagrangian of empty space-time accounts for gravity as an emergent feature from the microscopic structure of space-time. Once time has legitimately been introduced, a global positioning method based on local measurements of proper times between the arrivals of electromagnetic pulses from independent distant sources is presented. The method considers both pulsars as well as artificial emitters located on celestial bodies of the solar system as pulsating beacons to be used for navigation and positioning.
f(R)-theories of gravity are reviewed in the framework of the matter-antimatter asymmetry in the Universe. The asymmetry is generated by the gravitational coupling of heavy (Majorana) neutrinos with the Ricci scalar curvature. In order that the mechanism works, a time varying non-zero Ricci curvature is necessary. The latter is provided by f(R) cosmology, whose Lagrangian density is of the form {\cal L}(R)\sim f(R). In particular we study the cases f(R)\sim R+\alpha R^n and f(R)\sim R^{1+\epsilon}.
We discuss the possibility of identification of point-like gamma-ray sources (PGS) with small scale dark matter (DM) clumps in our Galaxy. Gamma-rays are supposed to originate from annihilation of DM particles in the clumps, where annihilation rate is supposed to be enhanced, besides higher density, due to smaller relative velocities $v$ of DM particles. We parameterized the annihilation cross section $\sigma_\text{ann}(v)$ in the form of an arbitrary power law dependence on the relative velocity $v$ with/without factor of Sommerfeld-Gamow-Sakharov, implying existence of a new Coulomb-like interaction. Adopting different parameters of cross section and clump, satisfying condition $\Omega\lesssim 0.2$ on density of DM particles of question, they are constrained from comparison with Fermi/LAT data on unidentified PGS as well as on diffuse $\gamma$-radiation; results are applied to concrete DM candidates. Such analysis is found to be sensitive enough to existing uncertainty in the density profiles of DM in the clump what can provide a tool for their test. Also we discuss possibilities when gamma-radiating clump changes visibly its position on celestial sphere and it is seen as a spatially extended gamma-source (EGS), what can be probed in future experiments like Gamma-400.
Neutrinos can play an important role in the evolution of the Universe, modifying some of the cosmological observables. In this contribution we summarize the main aspects of cosmological relic neutrinos and we describe how the precision of present cosmological data can be used to learn about neutrino properties, in particular their mass, providing complementary information to beta decay and neutrinoless double-beta decay experiments. We show how the analysis of current cosmological observations, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure, provides an upper bound on the sum of neutrino masses of order 1 eV or less, with very good perspectives from future cosmological measurements which are expected to be sensitive to neutrino masses well into the sub-eV range.
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We report on a measurement of the temperature of the cosmic microwave background radiation field, T_CMB, at z = 0.88582 by imaging HC3N (3-2) and (5-4) absorption in the foreground galaxy of the gravitationally lens magnified radio source PKS 1830-211 using the Very Long Baseline Array and the phased Very Large Array. Low-resolution imaging of the data yields a value of Trot = 5.6+2.5-0.9 K, for the rotational temperature, Trot, which is consistent with the temperature of the cosmic microwave background at the absorber's redshift of 2.73(1+z) K. However, our high-resolution imaging reveals that the absorption peak position of the foreground gas is offset from the continuum peak position of the synchrotron radiation from PKS 1830-211 SW, which indicates that the absorbing cloud is covering only part of the emission from PKS 1830-211, rather than the entire core-jet region. This changes the line-to-continuum ratios, and we find Trot between 1.1 and 2.5 K, which is lower than the expected value. This shows that previous, Trot, measurements could be biased due to unresolved structure.
Due to its proximity, the mass of the supermassive black hole in the nucleus of Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk that surrounds it. We report here the discovery of an eccentric Halpha emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0_{-1.0}^{+0.8} x 10^7 Mo for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1-sigma level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-sigma relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the Halpha emitting disk. This result suggests that the stellar and the Halpha emitting disks are intrinsically different from each other. A plausible explanation is that the Halpha emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the Halpha emission is, at least partially, generated by stars.
This paper presents a review of the topic of galaxy formation and evolution, focusing on basic features of galaxies, and how these observables reveal how galaxies and their stars assemble over cosmic time. I give an overview of the observed properties of galaxies in the nearby universe and for those at higher redshifts up to z~10. This includes a discussion of the major processes in which galaxies assemble and how we can now observe these - including the merger history of galaxies, the gas accretion and star formation rates. I show that for the most massive galaxies mergers and accretion are about equally important in the galaxy formation process between z = 1-3, while this likely differs for lower mass systems. I also discuss the mass differential evolution for galaxies, as well as how environment can affect galaxy evolution, although mass is the primary criteria for driving evolution. I also discuss how we are beginning to measure the dark matter content of galaxies at different epochs as measured through kinematics and clustering. Finally, I review how observables of galaxies, and the observed galaxy formation process, compares with predictions from simulations of galaxy formation, finding significant discrepancies in the abundances of massive galaxies and the merger history. I conclude by examining prospects for the future using JWST, Euclid, SKA, and the ELTs in addressing outstanding issues.
The Circumgalactic Medium (CGM) of late-type galaxies is characterized using UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph. CGM warm cloud properties are derived, including volume filling factors of 3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5 virial radii are metal-bearing and many have velocities consistent with being bound, "galactic fountain" clouds. For galaxies with L > 0.1 L*, the total mass in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total baryons in massive spirals and comparable to the baryons in their parent galaxy disks. This leaves >50% of massive spiral-galaxy baryons "missing". Dwarfs (<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon fraction), suggesting that many of their warm clouds escape. Constant warm cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3} K) support the inference that previous COS detections of broad, shallow O VI and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K) intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM clouds cannot account for all the "missing baryons" in spirals, the hot intra-group gas can, and could account for ~20% of the cosmic baryon census at z ~ 0 if this hot gas is ubiquitous among spiral groups.
If the Galactic WMAP radio haze, as recently confirmed by Planck, is produced by dark matter annihilation or decay, similar diffuse radio halos should exist around other galaxies with physical properties comparable to the Milky Way. If instead the haze is due to an astrophysical mechanism peculiar to the Milky Way or to a transient event, a similar halo need not exist around all Milky Way "twins". We use radio observations of 66 spiral galaxies to test the dark matter origin of the haze. We select galaxies based on morphological type and maximal rotational velocity, and obtain their luminosities from a 1.49 GHz catalog and additional radio observations at other frequencies. We find many instances of galaxies with radio emission that is less than 5% as bright as naively expected from dark matter models that could produce the Milky Way haze, and at least 3 galaxies that are less than 1% as bright as expected, assuming dark matter distributions, magnetic fields, and cosmic ray propagation parameters equal to those of the Milky Way. For reasonable ranges for the variation of these parameters, we estimate the fraction of galaxies that should be expected to be significantly less bright in radio, and argue that this is marginally compatible with the observed distribution. While our findings therefore cannot rule out a dark matter origin for the radio haze at this time, we find numerous examples (including the Andromeda Galaxy) where, if dark matter is indeed the origin of the Milky Way haze, some mechanism must be in place to suppress the corresponding haze of the external galaxy. We point out that Planck data will offer opportunities to improve this type of constraint in a highly relevant frequency range and for a potentially larger set of candidate galaxies.
In this Letter, we propose a new generalized Ricci dark energy (NGR) model to
unify Ricci dark energy (RDE) and XCDM. Our model can distinguish between RDE
and XCDM by introducing a parameter $\beta$ called weight factor. When
$\beta=1$, NGR model becomes the usual RDE model. The XCDM model is
corresponding to $\beta=0$. Moreover, NGR model permits the situation where
neither $\beta=1$ nor $\beta=0$. We then perform a statefinder analysis on NGR
model to see how $\beta$ effects the trajectory on the $r-s$ plane.
In order to know the value of $\beta$, we constrain NGR model with latest
observations including type Ia supernovae (SNe Ia) from Union2 set (557 data),
baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan
Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample and cosmic
microwave background (CMB) observation from the 7-year Wilkinson Microwave
Anisotropy Probe (WMAP7) results. With Markov Chain Monte Carlo (MCMC) method,
the constraint result is
$\beta$=$0.08_{-0.21}^{+0.30}(1\sigma)_{-0.28}^{+0.43}(2\sigma)$, which
manifests the observations prefer a XCDM universe rather than RDE model. It
seems RDE model is ruled out in NGR scenario within $2\sigma$ regions.
Furthermore, we compare it with some of successful cosmological models using
AIC information criterion. NGR model seems to be a good choice for describing
the universe.
We analyze the possibility to distinguish between quintessence and phantom scalar field models of dark energy using observations of luminosity distance moduli of SNe Ia, CMB anisotropies and polarization, matter density perturbations and baryon acoustic oscillations. None of the present observations can decide between quintessence or phantom scalar field models at a statistically significant level: for each model a set of best-fit parameters exists, which matches all data with similar goodness of fit. We compare the relative differences of best-fit model predictions with observational uncertainties for each type of data and we show that the accuracy of SNe Ia luminosity distance data is far from the one necessary to distinguish these types of dark energy models, while the CMB data (WMAP, SPT and Planck) are close to being able to distinguish them. Also a significant improvement of the large-scale structure data (e.g. Euclid or BigBOSS) will enable us to decide between quintessence and phantom dark energy.
We propose a method of calculation of the power spectrum of cosmological perturbations by means of a direct numerical integration of hydrodynamic equations in the Fourier space for a random ensemble of initial conditions with subsequent averaging procedure. This method can be an alternative to the cosmological N-body simulations. We test realizability of this method in case of one-dimensional motion of gravitating matter pressureless shells. In order to test the numerical simulations, we found an analytical solution which describes one-dimensional collapse of plane shells. The results are used to study a nonlinear interaction of different Fourier modes.
Sources generating most of the X-ray background (XRB) are dispersed over a wide range of redshifts. Thus, statistical characteristics of the source distribution carry the information on the matter distribution on very large scales. We test the possibility to detect the variation of the X-ray source number counts over the celestial sphere. A large number of Chandra pointings spread over both galactic hemispheres is investigated. A search for all the point-like sources in the soft band of 0.5 - 2 keV is performed, and statistical assessment of the population of sources below the detection threshold is carried out. A homogeneous sample of the number counts at fluxes above ~10^{-16} erg/s/cm^2 for more than 300 ACIS fields was constructed. The counts correlations between overlapping fields were used to assess the accuracy of the computational methods used in the analysis. It is shown that the source number counts vary between fields at the level only slightly larger than the fluctuation amplitude expected for the random (Poissonian) distribution. Nevertheless, small asymmetry between galactic hemispheres is present. The average number of sources in the northern hemisphere is larger than in the southern at the 2.75 sigma level. Also the autocorrelation function of the source density in both hemispheres are substantially different. Possible explanations for the observed anisotropies are considered. If the effect is unrelated to the observational selection, a large scale inhomogeneities in the distribution of X-ray sources are required. Correlations of the source number counts observed in the southern hemisphere could be generated by a coherent structure extending over 1200 Mpc.
The observational evidence for the acceleration of the universe demonstrates that canonical theories of gravitation and particle physics are incomplete, if not incorrect. A new generation of astronomical facilities will shortly be able to carry out precision consistency tests of the standard cosmological model and search for evidence of new physics beyond it. I describe some of these tests, focusing on the universality of nature's fundamental couplings and the characterization of the properties of dark energy. I will also comment on prospects for forthcoming ESA and ESO facilities in which the CAUP Dark Side team is involved.
The present-day Universe is highly magnetized, even though the first magnetic seed fields were most probably extremely weak. To explain the growth of the magnetic field strength over many orders of magnitude fast amplification processes need to operate. The most efficient mechanism known today is the small-scale dynamo, which converts turbulent kinetic energy into magnetic energy leading to an exponential growth of the magnetic field. The efficiency of the dynamo depends on the type of turbulence indicated by the slope of the turbulence spectrum v(l) \propto l^{theta}, where v(l) is the eddy velocity at a scale l. We explore turbulent spectra ranging from incompressible Kolmogorov turbulence with theta = 1/3 to highly compressible Burgers turbulence with theta = 1/2. In this work we analyze the properties of the small-scale dynamo for low magnetic Prandtl numbers Pm, which denotes the ratio of the magnetic Reynolds number, Rm, to the hydrodynamical one, Re. We solve the Kazantsev equation, which describes the evolution of the small-scale magnetic field, using the WKB approximation. In the limit of low magnetic Prandtl numbers the growth rate is proportional to Rm^{(1-theta)/(1+theta)}. We furthermore discuss the critical magnetic Reynolds number Rm_crit, which is required for small-scale dynamo action. The value of Rm_crit is roughly 100 for Kolmogorov turbulence and 2700 for Burgers. Furthermore, we discuss that Rm_crit provides a stronger constraint in the limit of low Pm than it does for large Pm. We conclude that the small-scale dynamo can operate in the regime of low magnetic Prandtl numbers, if the magnetic Reynolds number is large enough. Thus, the magnetic field amplification on small scales can take place in a broad range of physical environments and amplify week magnetic seed fields on short timescales.
We study CMB constraints on non-Gaussianity from isocurvature perturbations of general types. Specifically, we study CDM/neutrino isocurvature perturbations which are uncorrelated or totally correlated with adiabatic ones. Using the data from the WMAP 7-year observation at V and W bands, we obtained optimal constraints on the nonlinearity parameters of adiabatic and isocurvature perturbations. Our result shows that primordial perturbations are consistent with Gaussian ones at around 2 sigma level for above mentioned isocurvature modes.
An extra dark radiation component can be present in the universe in the form of sterile neutrinos, axions or other very light degrees of freedom which may interact with the dark matter sector. We derive here the cosmological constraints on the dark radiation abundance, on its effective velocity and on its viscosity parameter from current data in dark radiation-dark matter coupled models. The cosmological bounds on the number of extra dark radiation species do not change significantly when considering interacting schemes. We also find that the constraints on the dark radiation effective velocity are degraded by an order of magnitude while the errors on the viscosity parameter are a factor of two larger when considering interacting scenarios. If future Cosmic Microwave Background data are analysed assuming a non interacting model but the dark radiation and the dark matter sectors interact in nature, the reconstructed values for the effective velocity and for the viscosity parameter will be shifted from their standard 1/3 expectation, namely ceff=0.34 (+0.006 -0.003) and cvis=0.29 (+0.002 -0.001) at 95% CL for the future COrE mission data.
This paper is devoted to the study of Noether gauge symmetries of $f(T)$ gravity minimally coupled with a canonical scalar field. We explicitly determine the unknown functions of the theory $f(T),V(\phi), W(\phi)$. We have shown that there are two invariants for this model, one of which defines the Hamiltonian $H$ under time invariance (energy conservation) and the other is related to scaling invariance. We show that the equation of state parameter in the present model can cross the cosmological constant boundary. The behavior of Hubble parameter in our model closely matches to that of $\Lambda$CDM model, thus our model is an alternative to the later.
In a semi-numerical model of reionization, the evolution of ionization fraction is simulated approximately by the ionizing photon to baryon ratio criterion. In this paper we incorporate a semi-analytical model of galaxy formation based on the Millennium II N-body simulation into the semi-numerical modeling of reionization. The semi-analytical model is used to predict the production of ionizing photons, then we use the semi-numerical method to model the reionization process. Such an approach allows more detailed modeling of the reionization, and also connects observations of galaxies at low and high redshifts to the reionization history. The galaxy formation model we use was designed to match the low-$z$ observations, and it also fits the high redshift luminosity function reasonably well, but its prediction on the star formation falls below the observed value, and we find that it also underpredicts the stellar ionizing photon production rate, hence the reionization can not be completed at $z \sim 6$ without taking into account some other potential sources of ionization photons. We also considered simple modifications of the model with more top heavy initial mass functions (IMF), with which the reionization can occur at earlier epochs. The incorporation of the semi-analytical model may also affect the topology of the HI regions during the EoR, and the neutral regions produced by our simulations with the semi-analytical model appeared less poriferous than the simple halo-based models.
XMASS, a low-background, large liquid-xenon detector, was used to search for solar axions that would be produced by bremsstrahlung and Compton effects in the Sun. With an exposure of 5.6ton days of liquid xenon, the model-independent limit on the coupling for mass $\ll$ 1keV is $|g_{aee}|< 5.4\times 10^{-11}$ (90% C.L.), which is a factor of two stronger than the existing experimental limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are 1.9 and 250eV, respectively. In the mass range of 10-40keV, this study produced the most stringent limit, which is better than that previously derived from astrophysical arguments regarding the Sun to date.
Cluster properties do not seem to be changing significantly during their mature evolution phase, for example they do not seem to show strong dynamical evolution at least up to z~0.5, their galaxy red sequence is already in place at least up to z$\sim$1.2, and their diffuse light content remains stable up to z~0.8. The question is now to know if cluster properties can evolve more significantly at redshifts notably higher than 1. We propose here to see how the properties of the intracluster light (ICL) evolve with redshift by detecting and analysing the ICL in the X-ray cluster CL J1449+0856 at z=2.07 (discovered by Gobat et al. 2011), based on deep HST NICMOS H band exposures.We used the same wavelet-based method as that applied to 10 clusters between z=0.4 and 0.8 by Guennou et al. (2012). We detect three diffuse light sources with respective total magnitudes of H=24.8, 25.5, and 25.9, plus a more compact object with a magnitude H=25.3. We discuss the significance of our detections and show that they are robust. The three sources of diffuse light indicate an elongation along a north-east south-west axis, similar to that of the distribution of the central galaxies and to the X-ray elongation. This strongly suggests a history of merging events along this direction. While Guennou et al. (2012) found a roughly constant amount of diffuse light for clusters between z~0 and 0.8, we put in evidence at least a 1.5 magnitude increase between z~0.8 and 2. If we assume that the amount of diffuse light is directly linked to the infall activity on the cluster, this implies that CL J1449+0856 is still undergoing strong merging events.
We present multiwavelength X-ray, optical and radio study of the Fanaroff & Riley class I radio galaxy CTD 86 based on \xmm{}, \rosat{}, Sloan Digital Sky Survey (SDSS), Vainu Bappu Telescope (VBT) observations and the Faint Images of the Radio Sky at Twenty centimeters (FIRST) survey. X-ray emission from CTD 86 originates from two components - diffuse thermal emission from hot gas ($kT\sim 0.9\kev$, $n_e\sim 10^{-3}{\rm cm^{-3}}$, $L_X \sim 5\times10^{42}{\rm ergs s^{-1}}$ and size $\sim 186{\rm kpc}$), and a central point source representing the active nucleus. The hot gaseous environment of CTD 86 is similar to those found in galaxy groups or bright early-type galaxies. We found no clear signature of radio-lobes interacting with the diffuse hot gas. X-ray emission from the active nucleus is well described by an intrinsically absorbed ($N_H \sim 5.9\times10^{22}{\rm cm^{-2}}$) power law ($\Gamma \sim 1.5$) with a $2-10\kev$ luminosity $L_X \sim 2.1\times10^{42}{\rm ergs s^{-1}}$. CTD 86 has a weak optical emission line spectrum typical of type 2 active galactic nuclei (AGN). The nuclear X-ray, H$\alpha$, and radio luminosities of CTD 86 are lower than those of luminous AGN. We have measured the stellar velocity dispersion, $\sigma=182\pm8\kms$, of CTD 86 and estimated the mass of central black hole, $M_{BH}\sim 9\times 10^7{\rm M\odot}$, accreting at a rate of $\dot{m} = L_{bol}/L_{Edd} \sim 4\times10^{-3}$. For more detail see submitted pdf
We study the cosmological perturbations in teleparallel dark energy models in which there is a dynamical scalar field with a non-minimal coupling to gravity. We find that the propagating degrees of freedom are the same as in quintessence cosmology despite that variables of the perturbed vierbein field are greater than those in metric theories. The resulting growth evolution shows that gravitational interactions are enhanced during the unique tracker evolution of teleparallel dark energy models.
We study the link between the X-ray emission in radio-quiet AGNs and the accretion rate on the central Supermassive Black-Hole (SMBH) using a well-defined and statistically complete sample of 70 type1 AGNs extracted from the XMM-Newton Bright Serendipitous survey (XBS). To this end, we search and quantify the statistical correlations between the main parameters that characterize the X-ray emission (i.e. the X-ray spectral slope and the X-ray loudness), and the accretion rate, both absolute and relative to the Eddington limit (Eddington ratio). Here, we summarize and discuss the main statistical correlations found and their possible implications on current disk-corona models.
In this brief article, I summarize attempts with collaborators over the last couple of years to extend the Galileon idea in two important ways. I discuss the effective field theory construction arising from co-dimension greater than one flat branes embedded in a flat background - the multi-Galileons - and then describe symmetric covariant versions of the Galileons, more suitable for general cosmological applications. These generalized Galileons can be thought of as interesting four-dimensional field theories in their own rights, but the work described here may also make it easier to embed them into higher dimensional theories. I also briefly mention some intriguing properties, including freedom from ghosts and a non-renormalization theorem, that hint at possible applications in particle physics and cosmology
We find that the cold gas can be magnetically launched from the disc surface with the help of the radiation pressure if the angular velocity of the radiation pressure dominated accretion disc is greater than a critical value, which decreases with increasing the disc thickness H/R (radiation pressure). This indicates the force exerted by the radiation from the disc indeed helps launching the outflow. The rotational velocity of the gas in the disc depends on the strength of the magnetic field threading the disc and the inclination B_z/B_r of the field line at the disc surface. The launching condition for the cold gas at the disc surface sets an upper limit on the magnetic field strength, which is a function of the field line inclination B_z/B_r and the disc thickness H/R. This implies a more strict constraint on the maximal jet power can be extracted from a radiation pressure dominated accretion disc than that derived conventionally on the equipartition assumption.
We performed detailed investigation into cosmological perturbation of f(T) theory of gravity coupled with scalar field. Our work emphasizes on the exact way of gauge fixing and we examined all possible modes of perturbations up to second order. This includes in addition to the usual scalar, vector, and tensor modes, also pseudoscalar and pseudovector modes; although we find that there is no gravitational propagating degrees of freedom in the scalar, pseudoscalar, vector, as well as pseudovector modes. We also find that the scalar and tensor perturbations have exactly the same form as their counterparts in usual general relativity with scalar field, except that the factor of reduced Planck mass squared that occurs in the latter has now been replaced by an effective time-dependent gravitational coupling $-2 (df/dT)|_{T=T_0}$, with $T_0$ being the background torsion scalar. The absence of extra degrees of freedom of f(T) gravity at second order linear perturbation indicates that f(T) gravity is highly nonlinear, and one cannot conclusively analyze stability of the theory without performing nonlinear analysis that can reveal the propagation of the extra degrees of freedom.
The extragalactic background light (EBL) contains important information about stellar and galaxy evolution. It leaves imprint on the very high energy $\gamma$-ray spectra from sources at cosmological distances due to the process of pair production. In this work we propose to {\em measure} the EBL directly by extracting the collective attenuation effects in a number of $\gamma$-ray sources at different redshifts. Using a Markov Chain Monte Carlo fitting method, the EBL intensities and the intrinsic spectral parameters of $\gamma$-ray sources are derived simultaneously. No prior shape of EBL is assumed in the fit. With this method, we can for the first time to derive the spectral shape of the EBL model-independently. Our result shows the expected features predicted by the present EBL models and thus support the understanding of the EBL origin.
We have monitored the BL Lac object S5 0716+714 in five intermediate optical wavebands from 2004 September to 2011 April. Here we present the data that include 8661 measurements which represents one of the largest databases obtained for an object at optical domain. A simple analysis of the data indicates that the object was active in most time, and intraday variability was frequently observed. In total, the object varied by 2.614 magnitudes in the $i$ band. Strong bluer-when-brighter chromatism was observed on long, intermediate, and short timescales.
We report on the discovery of a new Milky Way companion stellar system located at (RA, Dec) = (22h10m43s, +14:56:30). The discovery was made using the eighth data release of SDSS after applying an automated method to search for overdensities in the Baryon Oscillation Spectroscopic Survey footprint. Follow-up observations were performed using CFHT-MegaCam, which reveal that this system is comprised of an old stellar population, located at a distance of 31.9+1.0-1.6 kpc, with a half-light radius of r_h = 9.27 +/- 0.88 pc and a concentration parameter of c = 0.82. A systematic isochrone fit to its color-magnitude diagram resulted in log(age) = 10.07+0.05-0.03 and [Fe/H] = -1.58+0.08-0.13 . These quantities are typical of globular clusters in the MW halo. The newly found object is of low stellar mass, whose observed excess relative to the background is caused by 96 +/- 3 stars. The direct integration of its background decontaminated luminosity function leads to an absolute magnitude of MV = -1.21 +/- 0.66. The resulting surface brightness is uV = 27.19 mag/arcsec2 . Its position in the M_V vs. r_h diagram lies close to AM4 and Koposov 1, which are identified as star clusters. The object is most likely a very faint star cluster - one of the faintest and lowest mass systems yet identified.
This talk discusses various aspects of the structure of space-time presenting mechanisms leading to the explanation of the "rigidity" of the manifold and to the emergence of time, i.e. of the Lorentzian signature. The proposed ingredient is the analog, in four dimensions, of the deformation energy associated with the common threedimensional elasticity theory. The inclusion of this additional term in the Lagrangian of empty space-time accounts for gravity as an emergent feature from the microscopic structure of space-time. Once time has legitimately been introduced, a global positioning method based on local measurements of proper times between the arrivals of electromagnetic pulses from independent distant sources is presented. The method considers both pulsars as well as artificial emitters located on celestial bodies of the solar system as pulsating beacons to be used for navigation and positioning.
f(R)-theories of gravity are reviewed in the framework of the matter-antimatter asymmetry in the Universe. The asymmetry is generated by the gravitational coupling of heavy (Majorana) neutrinos with the Ricci scalar curvature. In order that the mechanism works, a time varying non-zero Ricci curvature is necessary. The latter is provided by f(R) cosmology, whose Lagrangian density is of the form {\cal L}(R)\sim f(R). In particular we study the cases f(R)\sim R+\alpha R^n and f(R)\sim R^{1+\epsilon}.
We discuss the possibility of identification of point-like gamma-ray sources (PGS) with small scale dark matter (DM) clumps in our Galaxy. Gamma-rays are supposed to originate from annihilation of DM particles in the clumps, where annihilation rate is supposed to be enhanced, besides higher density, due to smaller relative velocities $v$ of DM particles. We parameterized the annihilation cross section $\sigma_\text{ann}(v)$ in the form of an arbitrary power law dependence on the relative velocity $v$ with/without factor of Sommerfeld-Gamow-Sakharov, implying existence of a new Coulomb-like interaction. Adopting different parameters of cross section and clump, satisfying condition $\Omega\lesssim 0.2$ on density of DM particles of question, they are constrained from comparison with Fermi/LAT data on unidentified PGS as well as on diffuse $\gamma$-radiation; results are applied to concrete DM candidates. Such analysis is found to be sensitive enough to existing uncertainty in the density profiles of DM in the clump what can provide a tool for their test. Also we discuss possibilities when gamma-radiating clump changes visibly its position on celestial sphere and it is seen as a spatially extended gamma-source (EGS), what can be probed in future experiments like Gamma-400.
Neutrinos can play an important role in the evolution of the Universe, modifying some of the cosmological observables. In this contribution we summarize the main aspects of cosmological relic neutrinos and we describe how the precision of present cosmological data can be used to learn about neutrino properties, in particular their mass, providing complementary information to beta decay and neutrinoless double-beta decay experiments. We show how the analysis of current cosmological observations, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure, provides an upper bound on the sum of neutrino masses of order 1 eV or less, with very good perspectives from future cosmological measurements which are expected to be sensitive to neutrino masses well into the sub-eV range.
Links to: arXiv, form interface, find, astro-ph, recent, 1212, contact, help (Access key information)