arXiv subjects

S. Casertano

Publications and source records attributed to S. Casertano.

At least 37 records · Page 2Linked to original sources

arXiv2008

Double-blind test program for astrometric planet detection with Gaia

We use detailed simulations of the Gaia observations of synthetic planetary systems and develop and utilize independent software codes in double-blind mode to analyze the data, including statistical tools for planet detection and different algorithms for single and multiple Keplerian orbit fitting that use no a priori knowledge of the true orbital parameters of the systems. 1) Planets with astrometric signatures $α\simeq 3$ times the single-measurement error $σ_ψ$ and period $P\leq 5$ yr can be detected reliably, with a very small number of false positives. 2) At twice the detection limit, uncertainties in orbital parameters and masses are typically $15%-20%$. 3) Over 70% of two-planet systems with well-separated periods in the range $0.2\leq P\leq 9$ yr, $2\leqα/σ_ψ\leq 50$, and eccentricity $e\leq 0.6$ are correctly identified. 4) Favorable orbital configurations have orbital elements measured to better than 10% accuracy $> 90%$ of the time, and the value of the mutual inclination angle determined with uncertainties $\leq 10^{\degr}$. 5) Finally, uncertainties obtained from the fitting procedures are a good estimate of the actual errors. Extrapolating from the present-day statistical properties of the exoplanet sample, the results imply that a Gaia with $σ_ψ$ = 8 $μ$as, in its unbiased and complete magnitude-limited census of planetary systems, will measure several thousand giant planets out to 3-4 AUs from stars within 200 pc, and will characterize hundreds of multiple-planet systems, including meaningful coplanarity tests. Finally, we put Gaia into context, identifying several areas of planetary-system science in which Gaia can be expected to have a relevant impact, when combined with data coming from other ongoing and future planet search programs.

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arXiv2007

Testing Planet Formation Models with Gaia $μ$as Astrometry

In this paper, we first summarize the results of a large-scale double-blind tests campaign carried out for the realistic estimation of the Gaia potential in detecting and measuring planetary systems. Then, we put the identified capabilities in context by highlighting the unique contribution that the Gaia exoplanet discoveries will be able to bring to the science of extrasolar planets during the next decade.

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arXiv2005

Star--forming galaxies at intermediate redshifts: morphology, ages and sizes

We present the analysis of the deepest near-UV image obtained with HST using the WFPC2(F300W) as part of the parallel observations of the Ultra Deep Field campaign. The U-band 10sigma limiting magnitude measured over 0.2 arcsec square is m(AB)=27.5 which is 0.5 magnitudes deeper than that in the HDF-North. We matched the U-band catalog with those in the ACS images taken during the GOODS observations of the CDF-South and obtained photometric-z for 306 matched objects. We find that the UV-selected galaxies span all the major morphological types at 0.2<z_phot<1.2. However, disks are more common at lower redshifts, 0.2<z_phot<0.8. Higher-z objects (0.7<z_phot<1.2) are on average bluer than lower-z and have spectral type typical of starbursts. Their morphologies are compact, peculiar or low surface brightness galaxies. The average half-light radius (rest-frame 1200--1800 A) of the UV-selected galaxies at 0.66<z_ phot<1.5 is 0.26 +- 0.01 arcsec (2.07 +- 0.08 kpc). The UV-selected galaxies are on average fainter (M_B=-18.43+-0.13) than Lyman Break Galaxies (M_B=-23+-1). Our sample includes early-type galaxies that are presumably massive and forming stars only in their cores, as well as starburst-type systems that are more similar to the LBGs, although much less luminous. This implies that even the starbursts in our sample are either much less massive than LBGs or are forming stars at a much lower rate or both. The low surface brightness galaxies have no overlap with the LBGs and form an interesting new class of their own.

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arXiv2005

Evidence for a Massive Post-Starburst Galaxy at z ~ 6.5

We present results from a search for high-redshift J--band ``dropout'' galaxies in the portion of the GOODS southern field that is covered by extremely deep imaging from the Hubble Ultradeep Field (HUDF).Using observations at optical, near-infrared and mid-infrared wavelengths from the Hubble and Spitzer Space Telescopes and the ESO-VLT, we search for very massive galaxies at high redshifts and find one particularly remarkable candidate. Its spectral energy distribution is consistent with a galaxy at z ~ 6.5 and a stellar mass of 6x10e11 M(sun) (for a Salpeter IMF). We interpret a prominent photometric break between the near-infrared and Spitzer bandpasses as the 3646A Balmer discontinuity. The best-fitting models have low reddening and ages of several hundred Myr, placing the formation of the bulk of the stars at z > 9. Alternative models of dusty galaxies at z ~ 2.5 are possible but provide significantly poorer fits. The object is detected with Spitzer at 24 micron. This emission originats from an obscured active nucleus or star formation. We present optical and near-infrared spectroscopy which has, thus far, failed to detect any spectral features. This helps limit the solution in which the galaxy is a starburst or active galaxy at z ~ 2.5. If the high-redshift interpretation is correct, this object would be an example of a galaxy that formed by a process strongly resembling traditional models of monolithic collapse, in a way which a very large mass of stars formed within a remarkably short period of time, at very high redshift.

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arXiv2004

The Hubble Higher-Z Supernova Search: Supernovae to z=1.6 and Constraints on Type Ia Progenitor Models

We present results from the Hubble Higher-z Supernova Search, the first space-based open field survey for supernovae (SNe). In cooperation with the Great Observatories Origins Deep Survey, we have used the Hubble Space Telescope with the Advanced Camera for Surveys to cover 300 square arcmin in the area of the Chandra Deep Field South and the Hubble Deep Field North on five separate search epochs (separated by 45 day intervals) to a limiting magnitude of z'=26. These deep observations have allowed us to discover 42 SNe in the redshift range 0.2 < z < 1.6. As these data span a large range in redshift, they are ideal for testing the validity of Type Ia supernova progenitor models with the distribution of expected ``delay times,'' from progenitor star formation to SN Ia explosion, and the SN rates these models predict. Through a Bayesian maximum likelihood test, we determine which delay-time models best reproduce the redshift distribution of SNe Ia discovered in this survey. We find that models that require a large fraction of ``prompt'' (less than 2 Gyr) SNe Ia poorly reproduce the observed redshift distribution and are rejected at 95% confidence. We find that Gaussian models best fit the observed data for mean delay times in the range of 3 to 4 Gyr.

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arXiv2004

The Nature of Faint 24 micron Sources Seen in Spitzer Observations of ELAIS-N1

The Spitzer Space Telescope has undertaken the deepest ever observations of the 24 micron sky in the ELAIS-N1 field as part of GOODS Science Verification observations. We present the shape of the 24 micron source counts in the flux range 20-1000 microJy, discuss the redshift distribution and nature of these sources with particular emphasis on their near-infrared counterparts.

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arXiv2003

Strong Gravitational Lens Candidates in the GOODS ACS Fields

We present results from a systematic search for strong gravitational lenses in the GOODS ACS data. The search technique involves creating a sample of likely lensing galaxies, which we define as massive early-type galaxies in a redshift range 0.3 < z <1.3. The target galaxies are selected by color and magnitude, giving a sample of 1092 galaxies. For each galaxy in the sample, we subtract a smooth description of the galaxy light from the z_{850}-band data. The residuals are examined, along with true-color images created from the B_{435}V_{606}i_{775} data, for morphologies indicative of strong lensing. We present our six most promising lens candidates, as well as our full list of candidates.

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arXiv2003

Narrow-Angle Astrometry with the Space Interferometry Mission: The Search for Extra-Solar Planets. II. Detection and Characterization of Planetary Systems

(Abridged) The probability of detecting additional companions is essentially unchanged with respect to the single-planet configurations, but after fitting and subtraction of orbits with astrometric signal-to-noise ratio $α/σ_d\to 1$ the false detection rates can be enhanced by up to a factor 2; the periodogram approach results in robust multiple-planet detection for systems with periods shorter than the SIM mission length, even at low values of $α/σ_d$, while the least squares technique combined with Fourier series expansions is arguably preferable in the long-period regime. The accuracy on multiple-planet orbit reconstruction and mass determination suffers a typical degradation of 30-40% with respect to single-planet solutions; mass and orbital inclination can be measured to better than 10% for periods as short as 0.1 yr, and for $α/σ_d$ as low as $\sim 5$, while $α/σ_d\simeq 100$ is required in order to measure with similar accuracy systems harboring objects with periods as long as three times the mission duration. For systems with all components producing $α/σ_d\simeq 10$ or greater, quasi-coplanarity can be reliably established with uncertainties of a few degrees, for periods in the range $0.1\leq T\leq 15$ yr; in systems where at least one component has $α/σ_d\to 1$, coplanarity measurements are compromised, with typical uncertainties on the mutual inclinations of order of $30^\circ-40^\circ$. Our findings are illustrative of the importance of the contribution SIM will make to the fields of formation and evolution of planetary systems.

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arXiv2003

The GAIA Astrometric Survey of the Solar Neighborhood and its Contribution to the Target Database for DARWIN/TPF

We evaluate the potential of the ESA Cornerstone Mission GAIA in helping populate the database of nearby stars ($d < 25$ pc) for subsequent target selection for DARWIN/TPF. The GAIA high-precision astrometric measurements will make it an ideal tool for a complete screening of the expected several thousands stars within 25 pc in order to identify and characterize (or rule out the presence of) Jupiter signposts. GAIA astrometry will be instrumental in complementing radial velocity surveys of F-G-K stars, and will more effectively search for massive planets the large database of nearby M dwarfs, which are less easily accessible with precision spectroscopy. The ability to determine the actual planet masses and inclination angles for detected systems, especially those with low-mass primaries (M $< 0.6$ M$_\odot$), stems as a fundamental contribution GAIA will make toward the final target selection for DARWIN/TPF, thus complementing exo-zodiacal dust emission observations from ground-based observatories such as Keck, LBTI, and VLTI.

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arXiv2002

Narrow-Angle Astrometry with the Space Interferometry Mission: The Search for Extra-solar Planets. I. Detection and Characterization of Single Planets

(abridged) We present results from a detailed set of end-to-end numerical simulations of SIM narrow-angle astrometric measurements and data analysis to illustrate the enormous potential that SIM has for the discovery and characterization of planets outside the Solar System. Utilizing a template observing scenario, we quantify SIM sensitivity to single planets orbiting single normal nearby stars as function of measurement errors and properties of the planet: SIM will detect over 95% of the planets with periods between a few days and the 5-year nominal mission lifetime that produce astrometric signatures $\sim 2.2$ times larger than the single-measurement accuracy. We provide accuracy estimates of full-orbit reconstruction and planet mass determination: at twice the discovery limit, orbital elements will be determined with a typical accuracy of 20-30%; the astrometric signature must be $\sim 10$ and $\sim 15$ times the minimum signal required for detection to derive mass and inclination angle estimates accurate to 10%. We quantify the impact of different observing strategies on the boundaries for secure detection and accurate orbit estimation: the results scale with the square root of both the number of observations and the number of reference stars. We investigate SIM discovery space, to gauge the instrument ability in detecting very low-mass planets: around the nearest stars, SIM will find planets as small as Earth, if they are present. Some of these might be orbiting inside the parent star's Habitable Zone. (abridged)

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arXiv2001

The evolution of field early-type galaxies to z~0.7

We have measured the Fundamental Plane (FP) parameters for a sample of 30 field early-type galaxies (E/S0) in the redshift range 0.1 5Åin 22% of an enlarged sample of 42 massive E/S0 in the range 0.1<z<0.73, in contrast with the quiescent population observed in clusters at similar z. We interpret these findings as evidence that a significant fraction of massive field E/S0 experiences secondary episodes of star-formation at z<1.

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arXiv2001

The GAIA astrometric survey of extra-solar planets

The ESA Cornerstone Mission GAIA, to be launched prior to 2012 and with a nominal lifetime of 5 years, will improve the accuracy of Hipparcos astrometry by more than two orders of magnitude. GAIA high-precision global astrometric measurements will provide deep insights on the science of extra-solar planets. The GAIA contribution is primarily understood in terms of the number and spectral type of targets available for investigation, and characteristics of the planets to be searched for. Several hundreds of thousands of solar-type stars (F-G-K) within a sphere of $\sim 200$ pc centered on our Sun will be observed. GAIA will be particularly sensitive to giant planets (M$_\mathrm{p}$$\sim$M$_\mathrm{J}$) on wide orbits, up to periods twice as large as the mission duration, the potential signposts of the existence of rocky planets in the Habitable Zone. Thousands of new planets might be discovered, and a significant fraction of those which will be detected will have orbital parameters measured to better than 30% accuracy. By measuring to a few degrees the relative inclinations of planets in multiple systems with favorable configurations, GAIA will also make measurements of unique value towards a better understanding of the formation and evolution processes of planetary systems.

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arXiv2001

The properties of field elliptical galaxies at intermediate redshift. III: the Fundamental Plane and the evolution of stellar populations from z~0.4 to z=0

We report on the study of a sample of 25 field early-type galaxies, in the redshift range z~0.1-0.5, selected on the basis of colours and morphology from the HST-MDS. Field early-type galaxies define a tight Fundamental Plane (FP) out to z~0.4, with scatter unchanged with respect to local samples, within the observational errors. The intermediate redshift FP is offset with respect to the FP of the Coma Cluster. The offset of the FP is found to increase with redshift. The evolution of the FP is studied quantitatively with a Bayesian-Montecarlo technique. By applying this technique, we find that the offset of the intercept of the FP (Δγ) with respect to the local FP increases as Δγ= τz with the following 68 per cent limits: 0.33<τ<0.44 (for Ω=1, Ω_Λ=0) or 0.44<τ<0.56 (for Ω=0.3,Ω_Λ=0.7). In addition, we interpret the results in terms of the evolution of the stellar populations, under the assumption of passive evolution. In a single-burst scenario, the observed properties are consistent with those of a stellar population formed at z>2 (for Ω=1, Ω_Λ=0, H_0=50 \kms Mpc^{-1}) or 0.8<z<1.6 (for Ω=0.3, Ω_Λ=0.7, H_0=65 \kms Mpc^{-1}). If a small fraction of the stellar mass is formed in a secondary burst, the primary burst may have occurred at higher z. Finally, the intercept and scatter of the FP found for field early-type galaxies and for cluster data at z~0.4 are mutually consistent, within the observational errors. If higher redshift (up to z=0.83) cluster data are considered, the ages of the stellar populations of field early-type galaxies inferred from a single-burst scenario are found to be marginally smaller than the ages derived for the cluster galaxies. [shortened]

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arXiv2001

Detection and measurement of planetary systems with GAIA

We use detailed numerical simulations and the $\upsilon$ Andromedae, planetary system as a template to evaluate the capability of the ESA Cornerstone Mission GAIA in detecting and measuring multiple planets around solar-type stars in the neighborhood of the Solar System. For the outer two planets of the $\upsilon$ Andromedae, system, GAIA high-precision global astrometric measurements would provide estimates of the full set of orbital elements and masses accurate to better than 1--10%, and would be capable of addressing the coplanarity issue by determining the true geometry of the system with uncertainties of order of a few degrees. Finally, we discuss the generalization to a variety of configurations of potential planetary systems in the solar neighborhood for which GAIA could provide accurate measurements of unique value for the science of extra-solar planets.

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arXiv2001

The properties of field elliptical galaxies at intermediate redshift. II: photometry and spectroscopy of an HST selected sample

A sample of field early-type galaxies (E/S0) at intermediate redshift ($z\sim0.1-0.6$) is selected, based on morphology and colours from HST-WFPC2 parallel images. Photometric structural parameters (effective radius $R_{\tx{e}}$ and effective surface brightness $SB_{\tx{e}}$) are derived through the F606W and F814W filters, using luminosity profile fitting and two-dimensional fitting techniques. The combined parameter that enters the Fundamental Plane ($\log R_{\tx{e}}-βSB_{\tx{e}}$, with $β\approx0.32$) is shown to suffer from significantly smaller uncertainties (r.m.s. 0.03) than the individual structural parameters (e.g. $\sim 15$ per cent r.m.s. on the effective radius). High signal-to-noise intermediate resolution spectra, taken at the ESO-3.6m, yield redshifts for 35 galaxies and central velocity dispersions for 22 galaxies. Central velocity dispersions are derived using a library of stellar templates covering a wide range of spectral types, in order to study the effects of templates mismatches. The average random error on the central velocity dispersion is found to be 8 per cent and the average systematic error due to template mismatch is found to be 5 per cent. The errors on velocity dispersion measurement and the effects of template mismatches are studied by means of extensive Montecarlo simulations. In addition, we investigate whether the determination of the velocity dispersion is sensitive to the spectral range used, finding that the value of velocity dispersion is unchanged when the spectral regions that include the absorption features Ca HK and NaD are masked out during the fit.

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arXiv2000

The Fundamental Plane of field early-type galaxies at intermediate redshift

We present preliminary results on the evolution of the stellar populations of field early-type galaxies (E/S0) from z=0.4 to z=0. The diagnostic tool used in this study is the Fundamental Plane (FP), a tight empirical correlation between their central velocity dispersion (sigma), effective radius (Re), and effective surface brightness (SBe), which is observed to hold in the local Universe. Using HST-WFPC2 archive images and spectra obtained at the ESO-3.6m telescope we measured the FP parameters for a sample of ~30 field E/S0s at z=0.2-0.4. Remarkably, field E/S0s at intermediate redshift also define a tight FP, with scatter unchanged with respect to that of local samples. The intermediate redshift FP is offset from the local one, in the sense that, for given RE and sigma, galaxies are brighter at z=0.4 than at z=0. The implication of the offset of the FP in terms of passive evolution of the stellar population depends on its star formation history. In a single burst scenario, the stellar populations of field E/S0s were formed at z=0.8-1.6 (Omega=0.3; Omega_{Lambda}=0.7; H_0=50 km/s/Mpc). Alternatively, the bulk of stars (90% in mass) can be formed at high redshift (z~3), and the rest in a secondary burst occurred more recently (z~0.5-0.8).

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arXiv2000

Space-borne global astrometric surveys: the hunt for extra-solar planets

The proposed global astrometry mission {\it GAIA}, recently recommended within the context of ESA's Horizon 2000 Plus long-term scientific program, appears capable of surveying the solar neighborhood within $\sim$ 200 pc for the astrometric signatures of planets around stars down to the magnitude limit of $V$=17 mag, which includes late M dwarfs at 100 pc. Realistic end-to-end simulations of the GAIA global astrometric measurements have yielded first quantitative estimates of the sensitivity to planetary perturbations and of the ability to measure their orbital parameters. Single Jupiter-mass planets around normal solar-type stars appear detectable up to 150 pc ($V\le $12 mag) with probabilities $\ge$ 50 per cent for orbital periods between $\sim$2.5 and $\sim$8 years, and their orbital parameters measured with better than 30 per cent accuracy to about 100 pc. Jupiter-like objects (same mass and period as our giant planet) are found with similar probabilities up to 100 pc.These first experiments indicate that the {\it GAIA} results would constitute an important addition to those which will come from the other ongoing and planned planet-search programs. These data combined would provide a formidable testing ground on which to confront theories of planetary formation and evolution.

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arXiv1999

HST Measurements of the Expansion of NGC 6543: Parallax Distance and Nebular Evolution

The optical expansion parallax of NGC 6543 has been detected and measured using two epochs of HST images separated by a time baseline of only three years. We have utilized three separate methods of deriving the angular expansion of bright fiducials, the results of which are in excellent agreement. We combine our angular expansion estimates with spectroscopically obtained expansion velocities to derive a distance to NGC 6543 of 1001$\pm$269 pc. The deduced kinematic age of the inner bright core of the nebula is 1039$\pm$259 years; however, the kinematic age of the polar caps that surround the core is larger - perhaps the result of deceleration or earlier mass ejection. The morphology and expansion patterns of NGC 6543 provide insight into a complex history of axisymmetric, interacting stellar mass ejections.

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